Abstract: With the continuous promotion of China's electricity market-oriented reform, the on-grid price of coal-fired power generation is formed by the market, and the power grid companies organize power purchase as the agency, which indicates that the market-oriented reform has entered a new stage. In provinces that do not actually operate the spot market, due to the cancellation of the base electricity, the power market lacks a supplementary mechanism to deal with the monthly deviation electricity. In this paper, the electricity composition of medium and long term power generation and the consumption is analyzed based on the situation that the power gird companies organize power purchase as the agency. Then the causes of medium and long term monthly electricity deviation is given. A market equilibrium model and three monthly balance mechanisms are proposed. An example simulation of a provincial power grid in East China is given to analyze their characteristics and adaptability. Finally, corresponding suggestions are put forward for China’s market design based on analysis of problems and development needs.