Abstract: Most megacities in China have entered the stage of metropolitan area (MA), but the domestic scholars had not paid enough attention to metropolitanization, and the related theory of MA is obviously lagging. In this context, the paper studies the metropolitan area planning since 1990s, including the concept, characteristics, spatial structure, optimization strategy, evolution mechanism and mechanism, etc. It is also found that the theory of metropolitan spatial structure is lacking, and the domestic scholars mainly analyze foreign cases at present. Polycentric spatial strategies have been widely recognized to space optimization, but it has poor academic basis. They have nearly joint thought that rail transit is beneficial to urban space reconstruction, but few quantitative analyses. Finally, it is put forward the concrete suggestions, including rules defining the metropolitan area, exploration of type and contents of MA in the context of China's urban space planning, exploration of how MA guides the rail line network, etc.