Abstract: To establish a perfect credit system for small and medium-sized enterprises is an effective way to solve the information asymmetry between banks and enterprises. Based on the service mode of the third-party credit reporting agencies, this paper constructs a dynamic game model among credit agencies, commercial banks and three SMEs to discuss the role of the third party′s credit information service and the choice of the operation mode of credit bureaus under different policy objectives. The results show that：（1）the introduction of credit bureaus will improve the efficiency of the credit market for SMEs-lowering market loan interest rate and increasing the total amount of credit, but the degree of influence of different service modes is different;(2)optimal service mode of credit institutions varies because of different policy objectives, and in profit maximization goal of credit institutions, it provides credit information only to small banks; in the goal of maximizing the remaining loan enterprise, it will provide credit information to large banks and small banks at the same time; in the social welfare maximization goal, it will determine depending on the degree of the bank lending threshold. At the present stage, the policy goal of China′s credit system construction is to maximum surplus of borrowing enterprises and maximization of social welfare, and credit agencies should choose to open paid information services to all banks; in the future, with the maturity of the credit service industry and the development of the market, private credit agencies will become the main body of the system, the maximization of profit will be the main policy goal, and the credit agencies can provide SMEs credit information to small and medium-sized banks.

Key words: SMEs, credit reporting agency, bank size, service mode, Cournot competition