It is generally acknowledged that it is difficult for the medium and small enterprises to get loan.On the basic of the theory of asymmetric inf ormation,the article analyzes the f inancing sources for the medium and s mall enterprises.It analyzes also the re ason why it is difficult for the mediu m and small enterprises to get loan using the theory of credit rations.Some polic y recommendations on relieving cred it rationing of the medium and small e nterprises are made.