Using the data from the 2012- 2013 Dynamic Monitoring Survey of National Migrant Population and city- level economic statistics, the paper investigates the effect of minimum wage increase on the overwork of low- paid rural migrant workers. We build a difference- in- differences multilevel model. The results show that the overwork of migrant workers is serious. The increase of minimum wage has contributed to increase the risk of overwork for the female migrant workers with no more than primary school education, and it also increases the extent of overwork for the male migrant workers with junior middle education. Therefore, it is vital for the government to reinforce the statutory working hours under the regulation of minimum wage, or to implement a minimum hourly wage. In addition, it is necessary to strengthen the implementation supervision on the minimum wage and legal working hour regulations. By combining the strict working hour regulations and controlling enterprises' overtime costs, we can reduce the negative impact effectively, and make the regulation of the minimum wage really play a role in protecting the low- paid groups.