The scale of public sector stock assets such as China’s infrastructure and public services is huge. The introduction of the PPP model of existing assets has put the existing assets under the management and operation of a more professional，more capable and experienced social capital party，helping to revitalize the public sector’s inventory assets，expand sources of investment and financing in the public sector，and provide social capital parties with more and better investment opportunities. However，in practice，the introduction of public domain stock assets into the PPP model faces many problems and constraints. In order to increase the attraction of existing assets to the social capital side from the source，the qualified social capital side is preferred to facilitate the smooth implementation of the existing asset PPP project，the planning and feasibility study and demonstration of the existing asset PPP project must be strengthened，and the scope of project cooperation and main transaction structure should be reasonably determined，sound investment return mechanism，perfect risk sharing mechanism，and scientifically set access conditions for the social capital side.