A method for differentiating the influences of the factors on the multiple stages of the decision on school children taking physical activity (PA) is proposed and tested using data collected from 403 parents in Shanghai, China, who provided information on their children’s PA and the perceived environment. The results show that accessibility to daily activity places is only associated with the PA engagement decision and safety-related factors are associated with the PA time decision and the decision of allocating PA time between moderate PA and vigorous PA. Some factors related to social environment and socio-economic status have opposite influences on the PA to the western literatures due to the specific cultural and societal contexts of contemporary China.