Since enacting the National Capital Construction Law in 1950, Japan has accumulated experience preparing metropolitan areas. In this paper, we analyze and collate the composition and contents of the laws related to territorial local planning, such as the National Spatial Planning Act and the improvement law of the three metropolitan areas. The second part of the study is devoted to regional plans and preparation plans of the three metropolitan areas, comparing their composition and main contents in terms of planning preparation and implementation, as well as explaining the characteristics of the “broad joint mechanism” of the three metropolitan areas. Finally, based on the experience of Japan’s metropolitan areas and the current situation of China’s metropolitan areas, the study draws inspiration from the legislative framework for planning, the formulation of territorial local plans, the guidance of land division, and the coordination of management mechanisms, to provide inspiration and reference for the smooth implementation of China’s metropolitan areas.