Relevant studies have shown that parent-child conflict has an important impact on children’s social adaptation [13]. According to attachment theory, the absence of a strong parent-child relationship during early life can have long-term implications on an individual’s developmental trajectory [7]. Considering that family factors may be an important impactor on NSSI in adolescents [14]. According to self-reports from adolescents, parent-child conflict emerges as one of the most prevalent triggers for NSSI [15]. Researchers found that intense parent-child conflict leads to emotional depletion and impaired self-control resources in adolescents, thus making adolescents who are already low in self-control prone to impulsive choices of NSSI to cope with stress [16]. High levels of parent-child conflict may result in unmet relational needs among adolescents, thereby eliciting negative emotions and prompting the adoption of maladaptive patterns that contribute to NSSI [15]. Additionally, according to the four-function model of NSSI, NSSI is a means of regulating emotions, cognitive experiences, communicating with or influencing others, and the presence of distal risk factors (e.g., child maltreatment) that lead to problems with emotion regulation and interpersonal communication increases the likelihood of NSSI occurrence [17]. In summary, this study puts forward the following hypothesis 1: Parent-child conflict exerts positive influences on NSSI in adolescents.

Depression has become one of the emotional problems that threaten the emotions and the development of sociality of adolescents [18]. The researchers believe that abnormal family relationships (such as abuse or neglect) are important factors for producing depression [19]. Previous studies have demonstrated a positive association between parent-child conflict and the development of depression in offspring [20]. A longitudinal study with a 15-year follow-up period revealed that parent-child conflict significantly increased the risk of adult offspring experiencing depression [21].

Moreover, studies have shown depression has a positive relationship with NSSI in adolescents [10] and that is an important predictive and dangerous factor for self-injury [22]. The risk of adolescent self-injury increases with anxiety and depression issues [10]. In addition, the four-function model of NSSI indicated that four processes maintain NSSI (i.e., NSSI may reduce or divert attention from unpleasant thoughts or sensations; NSSI may generate desired feelings or stimuli; NSSI may provide relief from an undesirable social situation; NSSI may encourage seeking help) [17]. Therefore, to alleviate depression, individuals might engage in self-injurious behaviors. In addition, previous studies also have shown that a poor family environment can increase adolescents’ NSSI behavior by increasing their depression [10]. In summary, we propose the following hypothesis 2: Depression may play a mediating role in the relationship between parent-child conflict and NSSI.

Based on the response styles theory, when individuals face stressors, there mainly are three coping styles: problem-solving, attentional shifting, and rumination [11]. Rumination thinking is associated with worse problem-solving abilities in individuals [23,24], which is a maladaptive response style and a habitual tendency and response to depressive emotions, involving repetitive and passive self-focus rather than thinking about how to solve problems [25]. Related studies have shown that adolescents who experience negative events in childhood are more inclined to use repeated negative coping styles to deal with negative emotions [26].

Meanwhile, rumination thinking, as a negative response style that makes the attention of individuals passively focused on adverse events, is associated with individual maladjustment [23]. Individuals exhibiting rumination thinking are prone to form negative cognitive patterns and continue to process information negatively about themselves and the outside world when facing negative events, which will increase the risk of depression [27]. Considering that individuals exhibiting elevated levels of rumination after parent-child conflicts display compromised problem-solving abilities. In the process, sadness, anger, and other experiences are constantly aggravated, and they are immersed in it for a long time and unable to take effective action [28], thereby increasing the likelihood of depression. In summary, the following hypothesis 3 is proposed: Rumination thinking plays a moderating role in the effect of parent-child conflict on adolescents’ depression.

In summary, based on the four-function model of NSSI and response style theory, this study explored the effects of parent-child conflict on adolescent NSSI and its mediating (depression) and moderating (rumination thinking) mechanisms. These findings are intended to provide theoretical support and practical guidance for future research on reducing NSSI among adolescents. The hypothesis model diagram is shown in Fig. 1.

The sample size was predetermined using Monte Carlo power analysis for indirect effects with a desired statistical power of 0.80 and a significance level of α = 0.05 [29]. Effect sizes derived from prior research were integrated to estimate the relationships between parent-child conflicts and NSSI (r = 0.28) [15], parent-child conflicts and depression (r = 0.39) [30], parent-child conflicts and rumination thinking (smallest effect size of r = 0.15), depression and NSSI (r = 0.40) [31], as well as rumination thinking and NSSI (r = 0.23) [32]. The results indicated that a total of 723 participants were required to adequately test the proposed model in this study, which employed a cluster sampling method. This study used a cluster sampling method, and 1240 adolescents were selected from four primary and secondary schools from Shandong Province, China as participants, and 13 of them were excluded for reasons such as not answering carefully. 1227 questionnaires were effectively recovered, and the recovery rate was 98.95% (male: 735, 59.90%; female: 492, 40.10%), the age distribution of the participants was 12–18 years old (13.11 ± 1.22).

The questionnaire method was employed in this study to collect scores on harsh parenting, depression, rumination thinking, and non-suicidal self-injury from participants on the SoJump platform. In addition, the procedures involving participants in this study were conducted in accordance with the ethical standards set by the Ethics Review Committee of Shangqiu Normal University and the 1964 Declaration of Helsinki [Ethics Approval Number: SQNU2005]. After obtaining informed consent from both participants and guardians, online questionnaire links were then sent to psychology staff who had received professional training for uniform distribution among students. Descriptive statistics (including the Mean and Standard Deviation), correlation analysis (the correlation relationship among variables), and reliability tests (Cronbach’s α of research instruments) were conducted using SPSS 26.0. Additionally, a moderated mediation model test (including path coefficient and the direct effect and indirect effect) was performed using PROCESS 3.3.

In this study, some items were expressed in reverse, and all questionnaires were filled in anonymously to control the possible common method bias in the test procedure. Moreover, the Harman single-factor test was employed to statistically examine the presence of common method biases [40]. The findings revealed that this study elucidated 14 factors with eigenvalues exceeding 1, accounting for a total variance interpretation of 68.248%. Notably, the first factor explained only 30.003% of the variance, which falls below the threshold of 40%. Consequently, it can be concluded that there is no significant evidence of common method biases in this study.

The results of correlation analysis showed that the intensity of parent-adolescent conflicts was significantly positively correlated with depression (r = 0.387, p < 0.001) and NSSI (r = 0.203, p < 0.001). And depression positively relates to the NSSI (r = 0.270, p < 0.001). The results are shown in Table 1.

The current study used the PROCESS model 7 to test the moderated mediation model, and the results showed that parent-child conflicts significantly impacted NSSI (β = 0.117, t = 2.845, p < 0.001), and depression (β = 0.382, t = 10.296, p < 0.001), depression significantly affected NSSI (β = 0.225, t = 4.321, p < 0.01). In addition, the direct effect of parent-adolescent conflicts on NSSI was 0.136, and the bootstrap 95% CI was [0.042, 0.229]; the indirect effect of depression on parent-adolescent conflicts and NSSI was 0.1, and the bootstrap 95% CI was [0.054, 0.168]. It is suggested that depression was a mediating mechanism of parent-child conflict and adolescents’ NSSI (see Table 2).

In addition, ruminative responses significantly impacted depression (β = 0.449, p < 0.001), and the interaction between parent-child conflict and ruminative responses significantly impacted depression (β = 0.096, p < 0.01). Ruminative responses may as a moderating mechanism of parent-adolescent conflicts on depression (see Table 3). Further simple slope analysis revealed a significant positive effect of parent-child conflict on depression among individuals with high rumination responses, simple slope = 0.289, t = 2.467, p = 0.014; for participants with low ruminative responses, the effect of parent-adolescent conflicts on depression was not significant, simple slope = 0.161, t = 1.617, p = 0.106, which indicated that with the improvement of individual ruminative responses, the influence of parent-child conflict on depression showed a gradually increasing trend (see Fig. 2).

The findings of the present study indicated that parent-child conflict had a positive effect on adolescents’ NSSI, which supports hypothesis 1. To a certain extent, this supports previous speculations about the influence of parent-child relationships on NSSI in adolescents, suggesting that the parent-child relationship is one of the most important interpersonal relationships for adolescents and that negative parent-child relationships increase the likelihood of NSSI [15]. The findings also further refine the four-function model of NSSI, which posits that NSSI serves as a mechanism for emotion regulation, cognitive processing, and interpersonal communication or influence [17]. Adolescents with negative parent-child relationships may harbor negative beliefs or maladaptive schemas, thereby placing them at an elevated risk of engaging in NSSI [15]. Furthermore, the act of participating in NSSI could serve as a coping mechanism for adolescents seeking to escape from oppressive, conflicting, or abusive circumstances [17]. Consequently, it is more probable for adolescents to resort to NSSI following experiences of parent-child conflict.

Meanwhile, the study revealed that depression serves as a mediating factor between parent-child conflict and NSSI in adolescents, thereby supporting hypothesis 2. Specifically, it was found that a negative family environment significantly predicts NSSI through the intermediary influence of depressive symptoms [22]. Previous studies have found that poor quality of attachment to parents, harsh punishment from parents, and low perception of social support are strongly associated with depression and other internalizing problems that predict self-injury behavior [41]. Additionally, existing research also found that family-relevant factors could increase adolescents’ NSSI by triggering their depression [30]. Adolescents growing up in dysfunctional or adverse family environments characterized by frequent parental conflicts are more prone to experiencing depression. This can lead to the adoption of maladaptive coping strategies due to a perceived lack of familial support, ultimately resulting in NSSI [42].

In addition, the study has also revealed that rumination thinking moderates the relationship between parent-child conflict and adolescents’ depression, thereby supporting hypothesis 3. This finding further substantiates the notion that rumination thinking could increase the possibility of experiencing depression after going through a negative event [43]. Previous research has demonstrated that rumination thinking moderates the process of depression induced by negative factors. For example, it can moderate the association between the excessive utilization of mobile phones/social networks and depression [44]. Moreover, these findings provide additional evidence to support the reactive style theory, suggesting that rumination serves as a pivotal vulnerability factor in the process of worsening depression [27], amplifying negative thinking patterns while impeding problem-solving abilities and eroding social support networks. Consequently, this may lead to greater maladjustment and exacerbate the likelihood of experiencing depressive symptoms [25]. Therefore, in the current study, parent-child conflict as a negative event for adolescents experiencing, individuals with high rumination thinking living in the environment of parent-child conflict, may have a higher likelihood of manifesting symptoms indicative of depression because the repeated negative thinking about the scenario of conflicts occurred between parents and themselves [12].

Firstly, the findings of various studies indicate that there is a positive correlation between parent-child conflict and the occurrence of NSSI behaviors among adolescents. This indicates that negative family relationships or family atmospheres have a detrimental impact on adolescent development. The family is the first place of individual socialization, parents are the initial and most important agents of socialization of children [45]. The family environment and the way parents treat their children can have a profound and lasting effect on adolescents. Therefore, parents need to tailor their parenting to their children’s needs, use more moderate intervention strategies, give their children a degree of autonomy, reduce the chances of parent-child conflict erupting, and create a positive family atmosphere [46], and reduce the likelihood of adolescents engaging in NSSI.

Furthermore, this study unveiled the mediating role of depression in the association between parent-child conflict and adolescent NSSI. Therefore, schools should prioritize students experiencing parent-child conflict or strained family relationships, create a conducive classroom environment, enhance support and care from teachers and peers for depressed students, and maintain frequent communication with students. These measures effectively reduce depression levels and prevent the development of NSSI in individuals facing parent-child conflict. In addition, schools should also consciously cultivate students’ psychological resilience, carry out group counseling, and educate students to vent their emotions reasonably to improve their mental health.

Finally, the present study further elucidated the moderating role of rumination thinking in the association between parent-child conflict and depression. The susceptibility of students to the influence of parent-child conflict, resulting in higher levels of depression, is particularly pronounced among those with elevated levels of rumination thinking. Therefore, schools should promptly screen students with high levels of rumination thinking, provide timely and positive psychological guidance or counseling, and offer better strategies for dealing with negative events. This will help prevent individuals with high levels of rumination thinking from increasing their levels of depression due to their inability to positively resolve the negative emotions caused by parent-child conflict.