Whether the aggregation of migrant students in schools will affect the academic development of local students is a valuable and practical problem. Based on the survey data of grade 9 students collected by CEPS2013-2014 (China Education Panel Survey) and the balance test, this article simulated scenario of random class-division within the same school by adding the fixed effect and deleting samples of non-random class-division, estimated the effect of the proportion of migrant students on the academic performance of local students