The application of supply chain bring us some questions which need to be solved immediately. Bullwhip effect is one of these. We can lighten bullwhip effect through information sharing. The enterprises in SC need long, balance relationship. From Game Theory, the relationship could get. Through the stock information sharing cost analysis of two-stage SC against no sharing, the information sharing is not only need but also efficiency. The core enterprise in SC should use the Principal-agent theory to pursue information sharing with other enterprises.