To explore the influence of self-efficacy on physical activity and the mediating role of exercise identity. Children"s physical activity questionnaire, general self-efficacy scale and exercise identity scale were used to investigate the students of two primary schools in Nantong City, Jiangsu Province and Pingliang City, Gansu Province. The results showed that the score of physical activity was higher in male, junior, non-only-child and western region. The higher the self-efficacy, the higher the exercise identity level, the higher the physical activity level; Exercise identity played a partial mediating role between self-efficacy and physical activity, and the mediating effect accounted for 60%. To some extent, this study explains the internal influence mechanism between children and adolescents" self-efficacy and physical activity, which can provide theoretical and practical basis for children and adolescents" physical activity intervention.