In the process of urbanization, China’s urban land expansion is faster than that of population expansion, but the performance of cities of different sizes is different. The land expansion of larger cities is relatively slow and the population growth is relatively fast, while the opposite is true for smaller cities. This paper constructs an analytical framework on the coordination mechanism of population and land expansion, and points out that the incongruity is mainly caused by the inconsistent size and change of the supply elasticity of land and labor. The empirical analysis shows that the elasticity of urban land supply is higher than that of labor supply, which leads to the land expansion faster than the population expansion; In the development trend, the elasticity of urban land supply is declining, while the elasticity of labor supply is increasing; with different types of cities, the elasticity of land supply in larger cities is lower than that in smaller cities, while the elasticity of labor supply is similar. At the end of this paper, the fundamental way to change the uncoordinated situation is to deepen the reform of registered residence and land system, and strengthen their coordination.