Objective:To investigate the relationship between family functioning and self-injurious behavior among primary school children, as well as the effects of teacher-student relationship and friendship quality.Methods:A questionnaire survey was conducted with 1 033 primary school children from grade four to six in Hunan province from March to April 2024, using the family APGAR index scale, the deliberate self-injury inventory, the teacher-student relationship subscale of the my class questionnaire, and the friendship quality questionnaire. Data were analyzed using SPSS 26.0 software for normality tests, descriptive statistics, chi-square tests, and Pearson correlation analyses. Confirmatory factor analysis was performed with AMOS 24.0, and moderated mediating effects were examined using the PROCESS 3.5 macro program.Results:(1) The prevalence of self-injurious behavior among the sampled children was 37.4% (359/958), with no significant gender difference ( χ2=0.01, P>0.05). However, the detection rate among grades was significantly different ( χ2=8.25, P<0.05, Cramer's V=0.09). (2) Self-injurious behavior was negatively correlated with family functioning, teacher-student relationship, and friendship quality ( r=-0.29, -0.25, -0.18, P<0.01). Among family functioning, teacher-student relationship and friendship quality, there was positive correlations between each other ( r=0.33-0.40, all P<0.01). (3) Teacher-student relationship partially mediated the relationship between family functioning and self-injurious behavior, with the mediating effect value accounting for 20%(-0.06/-0.30) of the total effect. (4) Friendship quality moderated the first stage of the mediating effect of teacher-student relationship on the relationship between family functioning and self-injurious behavior ( β=0.08, P<0.01). When children's friendship quality was higher, the predictive effect of family functioning on teacher-student relationship was significantly strengthened ( βsimple=0.30, P<0.001, 95% CI=0.21~0.38). Conclusion:Effective family functioning promotes positive teacher-student relationship in children, thereby reducing the risk of self-injurious behavior. This effect is notably stronger among children with higher-quality friendships.