Abstract: From system perspectives of human capital allocation,this paper has analyzed the problem of social mobility of rural migrants in cities.In cities,one of the important reasons that the rural migrants can not effectively change their social status through career transition is because the existing human allocation system has become an unfair mechanism of social mobility to rural migrants.Furthermore,the system has affected the social mobility of the second generation of the rural migrants.The paper has analyzed the relation between the access to human capital and the social mobility of the rural migrants from the aspects of education system,training system,personnel system and production system of certain units. The paper concludes that to improve the existing situation,it is far from enough to simply change the system of registered permanent residence.Reforming the.system of human capital allocation will play a key role in upgrading human capital level of the rural floating population and making them have more opportunities for social mobility.