Abstract: The study analyzes the current situation and stratification mechanism of migrant children's sports participation in middle school in China during the transition period based on the 2014—2015 data from the China Education Panel Survey(CEPS).Resultsshow that: 1) The migrant middle school students are inactive in sports participation, and sports participation is still socially stratified; 2) the families' social capital has a significant effect on sports participation of migrant children. In addition, the migrant children from public schools are more likely active participants; 3) there are different social stratification patterns in sports participation between rural migrant children and city migrant children. The main determinants of city migrant children are school factors, and the determinants of rural migrant children are family structures and social status. The study suggests that social structure and social institutions are important elements that effect participation in sports for migrant children. It is necessary to develop quality polices, and improve the family cultural capital of rural migrants to curb negative influences.