Party building is an important guide and starting point for community-level social governance. The experience of grassroots social governance in megacities can be summarized into four aspects：first，the leadership of the party should be highlighted in the reform of administrative system and the optimization of functions；Second，we should highlight the party’s organizational strength in the horizontal and vertical joint party organization system reconstruction；Third，the strong cohesion of the party is reflected in the multi-subject co-governance. Fourth，we should emphasize the implementation of the party under the social contradictions forecast and early warning of the normal intervention mechanism. The enlightening significance of the municipal social governance experience of megacities shows Guangzhou that the axial function of party building should be strengthened to highlight leadership，a strong party member team should be built to enhance the organizational power，the mode of consultation and co-governance should be innovated to strengthen cohesion，and the support of smart science and technology should be strengthened to enhance the executive power.