Abstract: Credit is one of the bottlenecks in the development of online auction.The online reputation feedback system has an important effect on eliminating information asymmetry and the adverse choice problems.The paper gives an analysis on the reason of adverse selection problems in online auction market first,and then sets up a mathematical model about reputation in online auction market based on repeated game theory.The results show that online reputation systems can incite the sellers to be honest,and reduce the adverse selection problems to some extent Analyze the mechanism of reputation in online auction market in order to offer a new thought for the online websites.

Key words: online auction, reputation, online reputation feedback systems, lemon market