Previous studies support the significant role of parental supervision in shaping adolescent behaviors. However, adolescent development is influenced by multiple interacting systems. Limited research has simultaneously explored the roles of school adjustment and parent marital relationship quality in explaining how parental supervision affects adolescent problem behavior. This study investigates the longitudinal relationship between parental supervision and adolescent problem behaviors, specifically examining the mediating role of school adjustment and the moderating role of parental marital relationship quality. We analyzed longitudinal data from the China Education Panel Survey (CEPS). The sample was restricted to 8,475 first-year middle school students (4,072 females) and their parents who provided valid data at both the baseline (T1) and the one-year follow-up (T2) assessments. Results showed that: (1) Parental supervision at T1 significantly predicted a reduction in adolescent problem behaviors at T2; (2) School adjustment at T2 significantly mediated the relationship between parental supervision at T1 and problem behaviors at T2; (3) Parents' marital relationship at T1 moderated the indirect relationship between parental supervision at T1 and adolescent problem behaviors at T2 through school adjustment. Specifically, higher marital quality strengthened the link between parental supervision and school adjustment, thereby enhancing the indirect effect. However, marital quality did not significantly moderate the direct effect of parental supervision on problem behaviors, meaning the overall total effect remained statistically unchanged by this moderator. These findings highlight the importance of considering both school and family subsystems in understanding adolescent behavior, offering theoretical insights for ecological models and practical implications for family-school collaborative interventions.