To explore the influence and mechanism of parent-child relationship on adolescents' problematic smartphone use, a sample of 3355 Chinese adolescents ( =16.93,  = 0.49, range: 14-19 years old; 48% boys) is recruited to measure parent-child relationship, problematic smartphone use, personal growth initiative, and school belonging. The results are as follows. (1) After controlling for gender, age and time spent online per day, parent-child relationship is negatively correlated with problematic smartphone use, and the negative association between parent-child relationship and problematic smartphone use is mediated by the personal growth initiative. (2) The association between parent-child relationship and problematic smartphone use, the association between parent-child relationship and personal growth initiative, and the association between personal growth initiative and problematic smartphone use are all moderated by school belonging and are stronger in adolescents with a high level of school belonging. The present study highlights the mediating role of personal growth initiative and the moderating role of school belonging in the association between parent-child relationship and problematic smartphone use. This study also contributes to a better understanding of the effects, paths, and conditions of parent-child relationship on the problematic smartphone use of adolescents and provides constructive suggestions for preventing adolescents' problematic smartphone use in the mobile Internet era.