Lacking of physical exercise is relatively common phenomenon among adolescents，and it has also attracted great attention from the Chinese government. Based on the literature review of the status and associated factors of physical exercise among adolescents，our study recruited freshmen in a university in Beijing as an example and adopted social support theory in order to explore the influence of the support from family，peers and school on physical exercise behaviors of college students. It was found that the behaviors of physical exercise among students in this school were positively associated with the modeling effect and emotional support from their peers，and was also related to their healthy eating behaviors. Therefore，in order to improve the exercise level of adolescents，it is necessary to strengthen the support activities from families，peers and schools，especially peer support.