Abstract: Using a two-stage game model, this paper proves that repeated game can realize cooperation equilibrium under asymmetry information. Taobao is a platform helping buyers and sellers building trust each other. The sellers will have a good reputation which will get more orders if he would be honest, or be punished if dishonest. Reputation provides incentives to achieve cooperation equilibrium. Taobao sets up a guarantee system to keep away the opportunism of the buyers. The case of Taobao not only provides a sample of solving the trust problems of network, but also gives a good sample to our society.