Abstract: By using the methods of literature review, interview and comparative analysis, this paper makes a two-year participant?observation on 11 public primary schools, 9 residential areas, 8 community recreation centersand?more than 30 children's playgrounds in parks and communities in four school districts in Columbus, Ohio, USA, and analyzes the characteristics of the promotion mechanism of extracurricular physical activities of children aged 5～12 in the United States from a socio-ecological perspective. The characteristics can be summarized as follows: Individual level: the highest purpose of participating in sports is to let children " Have Fun"; Interpersonal level: close the relationship circle?between people , especially parents agree that "sports is an active and healthy lifestyle";?Community level: a community ecological support network of "family, school and integration of community" has been built;?Social level:?a cross-boundary, interconnected and efficient policy implementation system has been created. The implications for a socio-ecological construction of the same nature in China can be summarized as follows: Academic circles should strengthen the theoretical and practical research on the socio-ecological model of children's extracurricular physical activities with Chinese characteristics, and all relevant government departments should join efforts to create a cross-border, interwoven and efficient mechanism for such construction.