The study aimed to explore the development trend of positive mental health and the interaction between adolescents' perceived family support and positive mental health. A 3-year longitudinal survey of perceived family support and positive mental health (resilience and self-efficacy) for four waves was conducted with 564 junior high school students (297 girls, mean age = 11.12 ± 0.38 years at baseline). The Latent Growth Curve Modeling indicated that adolescents' resilience and general self-efficacy showed a curve upward trend, which increased first and then decreased. The development rate decreased each year. The cross-lagged panel model and a random intercept cross-lagged panel model concluded that perceived family support was strongly associated with positive mental health of junior high school students. Family support was important for developing positive mental health in early adolescence. Therefore, attention and interventions targeting positive mental health changes in early adolescence are particularly effective. And, it is important to encourage parents of adolescents to continue to provide support and guidance.