Under Chinese market-oriented process, medium-sized and small enterprises (SME) develop rapidly and are confronted with financing troublesome problem for a long range at the same time, and our country cultivates energetically guarantee organization in order to solve SME financing problems in recent years. This paper tries to study the risk mechanisms of SME bank financing process by information asymmetry and game theory. Results are as follows: SME financing possibility is related to enterprise scale, and changes also with continued period of enterprise in the same direction. Under the lack of public credit systems, credit guarantees can not have an effect to boost a financing development, the effect is restricted, but if all finance property rights such as loans from bank had got effective protection, to develop SME financing guarantee organization is really an effective.