Abstract: Education is a key issue affecting child development. Since the economic reform，the urban migration has continued its expansion in China. With the improvement in economy and transportation，the cost of household migration has fallen continuously，making family migration a prevailing model. Previous studies on migrant children's academic performance have mainly focused on the impact of family background and school environment and have neglected the important role of language environment. Using the data from the 2014 to 2015 China Education Panel Survey，this study examines the influence of migrant student dialect language ability on academic performance and the potential mechanism involved. We find that mastering local dialects can significantly improve migrant students' academic performance in two subject areas of Chinese and English. After checking the issue of estimation bias with various methods of instrumental variables，propensity score matching and sample selection，we find that the conclusion remains valid. The positive effect of dialect language ability does show differences in gender and region. In addition，support from teachers and classmates is identified as the mechanism by which academic performance is enhanced by mastering dialects. The mediation effect results，estimated based on the Bootstrap method，are consistent with the above finding. This study reveals the logic of the accumulation process of human capital of migrant children from the perspective of language environment. It provides references for governmental educational policy improvement for migrant children. This study expands the existing literature in three ways：first，the analysis of social integration in the existing research mainly concentrates on individual weakness at the micro-level and institutional exclusion at the macro-level. However，because dialects reflect both individual ability and macro-environment，this study has expanded the scope of the existing research on social integration. Second，this study introduces a new interpretation for the formation and changes of human capital of migrant children，as well as the interactive role of dialects，from a language perspective，unlike the common approaches of family and school system applied in the existing literature. Third，this study emphasizes the sociological significance of dialects in helping individuals integrate into new places and new cultural environment and accumulate personal capital，a perspective different from the existing literature's mere emphasis on the economic impact of dialects.

Key words: migrant children, dialect ability, academic performance, school integration, social support