<p>Physical activity is highly correlated with social media dependence in adolescence, but the underlying mechanisms between these variables require further investigation. This study suggests two potential psychological pathways linking physical activity and social media dependence in adolescence, with depression potentially serving as a mediating factor and difficulty describing feelings acting as a moderating factor. A self-reported survey was conducted with 3,247 Chinese adolescents, including measures of physical activity, social media dependence, depression, and difficulty describing feelings. Descriptive statistics and correlation analyses were performed on these variables, and a mediation-moderation model was developed. Physical activity showed a significant negative correlation with social media dependence, depression, and difficulty describing feelings. Additionally, depression was positively correlated with both social media dependence and difficulty describing feelings, and difficulty describing feelings was positively correlated with social media dependence. Furthermore, difficulty describing feelings moderated the relationship between depression and social media dependence in adolescence. This study provides further insights into the psychological mechanisms underlying the relationship between physical activity and social media dependence in adolescence. Depression serves as a mediating factor, while difficulty describing feelings acts as a moderating factor in the relationship between depression and social media dependence. These findings enhance our understanding of the role of depression and difficulty describing feelings in the relationship between physical activity and social media dependence, offering valuable implications for more comprehensive and targeted interventions aimed at reducing social media dependence among adolescents.</p>