In order to reduce the risk of large losses caused by power deviation assessment, a piecewise linear power assessment mechanism is proposed. Considering the four power purchase modes of bilateral contract market, centralized bidding market, independent power generation and demand side response, the power purchase and sales optimization model of power sales companies are put forward. Using the conditional value-at-risk method, a riskaversion optimization model is proposed to analyze the optimal power purchase combination of power sales companies considering risk aversion factors.