Based on 2011-2018 China Migrants Dynamic Survey （CMDS） of the National Health Commission，the paper research shows that the family size of migrants in megacities has an “inverted U-shaped” changing process since 2011，and compared with the national level，the average education time of migrants in megacities has also increased year by year. Rural migrants is still the largest part of internal migrants，and the ratio of urban migrants increases every year，however，the proportion of rural migrants shows a decreasing trend，especially in megacities. In these huge cities，internal migrants mainly move between provinces，while those migrants in some megacities with a permanent resident population of 5-10 million moves between provinces and cities within the same province，many of those migrants pay more attention on elder and children who move with them，and the latter is greater than the former. The willingness of rural migrants to stay is obviously small than the urban ones. From the perspective of income，employment and social security，the nominal wage premium in megacities is greater than other large cities. The migrant in megacities is mainly engaged in consumer service sectors，and most of them are employed in private enterprises. For social security，such as medical care，the proportion of migrants’ medical insurance in megacities is higher than that in other cities，however，for the selection of medical insurance place，rural migrants mainly choose original Hukou location，while urban migrants prefer to choose the current staying city. The paper further clarifies some typical facts of labor market characteristics of internal migrants in China’s megacities.