Despite the growing evidence that stressful life events are associated with adolescent non-suicidal self-injury (NSSI), few studies have investigated the mediating and moderating mechanisms underlying this link. The current study examined whether sleep quality mediated the link between stressful life events and NSSI and whether this mediating process was moderated by adolescent sensation seeking. The participants were 1006 Chinese adolescents (48.21% boys; mean age = 13.16 years, SD = 0.67). They completed the Life Events Checklist, Pittsburgh Sleep Quality Index, UPPS-P Impulsive Behavior Scale, and NSSI Questionnaire. The PROCESS macro for SPSS was used to examine the hypothesized moderated mediation model. The results showed that sleep quality significantly mediated the positive association between stressful life events and adolescent NSSI. Moreover, this mediating pathway was moderated by sensation seeking. Specifically, the risk impact of stressful life events on NSSI through sleep quality was significant only among adolescents with high-level sensation seeking but not among those with low-level sensation seeking. These findings provide intervention insights to reduce the risk of adolescent NSSI.