The increasing aging has put forward many challenges to the oldage service in China's big cities.S is the city with the most serious aging in China. Due to the main body positioning problems such as the poor government leadership, the insufficient market supply, the inadequate participation of social forces and the weakening of family pension function, it has fallen into the dilemma of “decoupling” of pension service supply and demand. Therefore, it is necessary to introduce the theoretical paradigm of welfare pluralism to reshape the role of the main body of pension services in big cities. The government should clearly define the role of leader, funder and builder, focus on the basic pension services, pay attention to policy formulation and debugging, and promote the construction of professional talent team. The market should clarify the role of effective supplier and pioneer, and aim at the effective supply of personalized pension services. The society should define the role of linker and innovator, aiming at resource integration and professional services. And family should define the role of buyer and supervisor, aiming at the financial support of the elderly and the quality supervision of purchased services.