Bullying victimization is a major risk factor for adolescents’ school adjustment, yet the mechanisms linking these experiences remain unclear. This study examined whether psychological resilience mediates the association between bullying victimization and school adjustment among junior high school students, and whether physical activity moderates this process. Using a cross-sectional design, data were obtained from 19,149 junior high school students in the Adolescent Health Theme Database. Regression, Bootstrap mediation, and moderated mediation analyses were conducted. Bullying victimization significantly and negatively associated with school adjustment (β = −0.460, p < 0.001). Psychological resilience partially accounted for this association: bullying victimization was negatively associated with psychological resilience (β = −0.314, p < 0.001), and psychological resilience was positively associated with school adjustment (β = 0.472, p < 0.001). The indirect effect was −0.149, with a 95% confidence interval of −0.157 to −0.140, accounting for 32.391% of the total effect. Physical activity moderated both the direct association between bullying victimization and school adjustment (β = 0.055, p < 0.001) and the association between psychological resilience and school adjustment (β = 0.020, p < 0.001). These findings indicate that bullying victimization is negatively associated with school adjustment, both directly and indirectly through its association with psychological resilience. Physical activity may serve as a modest but statistically significant protective factor by attenuating the adverse association between bullying victimization and school adjustment and strengthening the positive association between psychological resilience and school adjustment.