Increasing research has indicated associations between popularity goal and adolescents' social functioning. However, little is known about the processes intervening and moderating these associations. We examined whether popularity status insecurity explained the longitudinal associations of popularity goal with depression and social behavior among Chinese adolescents (N = 418), while also considering the moderating roles of initial popularity status and its changes. Results showed that popularity goal was positively related to popularity status insecurity. Moreover, popularity goal predicted greater relational aggression only when initial popularity was high, and popularity status insecurity predicted greater relational aggression only when popularity status was declining over time. Furthermore, popularity goal predicted greater depression through the mediation of popularity status insecurity when popularity status was initially lower and falling. The present findings highlight the complex interplay of social cognitive processes regarding popularity and variabilities of popularity in predicting adolescents' mental health and social behavior.