China experienced an early arrival of aged society around the turn of the century due to its rapid demographic transition．In order to keep the equilibrium development of population，it is essential to address the dilemma of the large population size and the unbalanced population structure under cer- tain resource，technology and institution conditions．If the government implements the universal two- child policy in time，and further adjusts the population and related socio-economic policies to increase TFＲto about 1. 8 and then gradually make it return to the replacement level，a stable population will be approximately achieved in the next 30 or 40 years．The age structure，together with the urban and rural composition will both reach a stable level．The proportion of population aged 60 or over will reach one- third，which is almost the average level of developed countries as a whole but still lower than that of Germany and Japan，and the urbanization rate will reach 75 percent．At that time，the human capital accumulation will rank forefront among the world，the modernization will be realized，and the balance among the factors of population itself and the development of economy，society，resources and envi- ronment is expected to be maintained．

China experienced an early arrival of aged society around the turn of the century due to its rapid demographic transition．In order to keep the equilibrium development of population，it is essential to address the dilemma of the large population size and the unbalanced population structure under certain resource，technology and institution conditions．If the government implements the universal two- child policy in time，and further adjusts the population and related socio-economic policies to increase TFR to about 1. 8 and then gradually make it return to the replacement level，a stable population will be approximately achieved in the next 30 or 40 years．The age structure，together with the urban and rural composition will both reach a stable level．The proportion of population aged 60 or over will reach one- third，which is almost the average level of developed countries as a whole but still lower than that of Germany and Japan，and the urbanization rate will reach 75 percent．At that time，the human capital accumulation will rank forefront among the world，the modernization will be realized，and the balance among the factors of population itself and the development of economy，society，resources and envi- ronment is expected to be maintained．

This paper examines the destination choice of migrants from a cost-benefit perspective, using binary logit models to explain why the megacities are so popular to be their destination. The results show that the net revenue, particularly different wage levels the floating individuals expect has great impact on their destination choices, which validates an important fact that high-wage income or that the huge wage gap between different regions is an important reason why migrants flowing into megacities. The total expenditure of floating migrants in Beijing, Shanghai and Guangzhou does not inhibit their flowing into these large cities. Implications of the results are that rather than taking measures to raise the cost of living in the cities to limit the floating population, it is better to make efforts in developing neighboring regions to attract more enterprises, create more jobs, and improve public services, thus redirecting the migrants in choosing their destination.