The rise of obesity rate brings serious threat to public health, but the effective physical activities can reduce the incidence of such chronic diseases as obesity, high blood pressure, cardiovascular disease and so on and is an important way for improving human health, and the boosting of physical activity level of the residents has become serious challenge of many countries in the world. The built environment is the reflection of urban planning and construction and is an important carrier affecting the physical activity and health of city residents. The existing research shows that the built environment can produce serious impact on physical activity and obesity. By taking the main districts of Chongqing as an example, by taking adult working group as research object, this paper supposes that the built environment affects their physical activity of transportation and their leisure physical activity, and further impacts their obesity situation. The research results show that there is significant relation between body mass index (BMI) of adult working group and the built environment variables such as the commute distance, the distance between public transport station and residence working place, the distance between the nearest physical activity place and residence dwelling place (or working place), and the frequency of going to physical activity places in a week. And finally this paper proposes to optimize the built environment, strengthen the physical activities of adult working group and reduce obesity incidence.