This study measured the coordinated development extent of population and economy using the data of last three national population censuses and socio-economic panel data of 21 megalopolises，and analyzed the key population factors affecting the quality of economic development. It is found that the coordinated development of megalopolises is generally on the rise with obvious regional differences，and population has become a main factor influencing the coordinated development of economy and population for most cities，where the percentage of college graduates and the number of postgraduate students are significant demographic factors behind high-quality economic development. To improve the coordination of economy and population in megalopolises，suggestions for promoting urban demographic development are proposed.