Introduction  The electricity sales company faces the fluctuation of electricity price in the spot market of the wholesale side and the uncertainty of the demand power of the retail side. In order to balance the benefits and risks， it is necessary to determine a reasonable proportion of electricity purchase in the medium and long-term market and the spot market and the time-of-use electricity price for consumers.

  Method  The demand price response curve was used to simulate the contesting of electricity sales companies in the medium and long-term contract market， and a quantitative method of transaction risk loss index based on conditional value at risk （CVaR） was proposed.

  Result  The demand response based on virtual power plant is realized through flexible load and distributed power generation， so as to balance the power deviation and the risk of price fluctuation in the spot market. On this basis， a two-level optimization model considering the power purchase strategy of electricity sales companies in the wholesale side market and the revenue of power selling on the retail side is established， and the crisscross optimization algorithm is used for solving the problem.

  Conclusion  The simulation results show the effectiveness of the method.