Abstract: With the reform of public medical institutions performed in China in late 1990s,the number of the private medical institution increases quickly. Although the privatization in public medical institutions plays a role in raising the supply of public healthcare resources,improving the efficiency of medical institutions and relieving the financial burden of the state,the adverse consequences emerge frequently. It is necessary to study the type and the cause of privatization in public medical institutions. Firstly,the paper defines the connotation of privatization in public medical institution and analyzes the possibility and the access to privatization. Secondly,the paper analyzes all kinds of risks in the health service system which is established in the relation between the medical institution and the patient. The paper concludes the risks,such as new monopoly risk,supervision risk,soft constraint risk,social justice and so on. At the same time,the paper points out that the risks are rooted in the inner risks of the actors and the unbalanced relation among the actors.