This study aims to provide a new perspective on the relationship between problematic Internet use and externalizing problem behavior among adolescents. Many studies have focused on the relationship between problematic Internet use and adolescent externalizing problem behavior; however, research on the underlying mechanism remain understudied. Altogether, 1161 Chinese rural adolescents aged 13-17 years completed a self-report questionnaire. The results indicate that: (1) Problematic Internet use has a negative effect on rural adolescent externalizing problem behaviors; (2) mental health has an effect on the relationship between problematic Internet use and externalizing problem behaviors; and (3) parental knowledge may moderate the indirect effect by attenuating the relationship between problematic Internet use and externalizing problem behaviors. Regarding these findings, this study has discussed the potential reasons and provided some practical suggestions to improve problematic Internet use among rural adolescents.