In the construction of China's public cultural service system, we should adhere to the combination of government leading and Participation of social forces. The effective interaction between government and social forces has a direct impact on the efficiency of public cultural service. This paper focuses on the interaction mechanism between the government and the Social forces in the supply of public cultural services, taking the "country stage" construction of Z city as an example. It is found that the different stages of interaction between government and society forces ,which has different interaction mechanism. First of all, the interaction between the government and social forces comes from the government mobilization, with policy guidance, administrative promotion and resource integration as the realization mechanism; the cooperative supply in the interactive operation stage is based on Complementary and enhancement as the basis ,project’s operation as the way, and the supervision as the guarantee. With the promotion of multi-agent cooperation, the deepening stage of collaborative governance mainly realizes organic interaction by Socialization and encouraging the masses to participate in the construction management. In the future, there will be many obstacles in the effective interaction between the government and social forces in the supply of public cultural services in China. It is still necessary to continue to increase the exploration on the theoretical and practical levels, so as to finally realize the co-construction and sharing of cultural governance pattern.