A price determination mode for large consumers is proposed under the present environments with large consumers purchasing electric power from the electricity supply utility in some area in Yunnan. With abundant waterpower in Yunnan, most of consumed electric power of large consumers is signed in the form of contracts. The contract price is determined by optimizing resources and maximizing profits of the supply utility. The different price is in accordance with different demand-price elasticity of large consumers. The difference between planned and actual consumption power is balanced in two spot markets. Because of the randomicity of spot price and trading power, the sale price of the supply utility in spot market is calculated based on stochastic programming. At last, simulation verifies the rationality of the models, which solves a part of problems faced by the supply utility in selling electricity to large consumers.