The contract coordination issue of a three-echelon supply chain is studied, which consists of the single supplier, the manufacturer and the retailer based on both the supplier and manufacturer random yield and the retailer random demand. The optimal decision models of the supply chain system are established and analyzed under the condition of centralization and decentralization. By using the risk-sharing contract, the expected profit of decentralization can be proved to be at the level of that of centralization decision based on random yield and demand. Finally, the analysis of the parameter of model and contract in the numerical example show the effectiveness of the risk-sharing contract coordination.