At present, the construction of China’s electricity market is still in its infancy, and the dual-track operation of planning and market will last for a long time. To explore the market liberalization scale under the dual-track system, it is necessary to study the calculation method of the medium-and-long-term trading power liberalization scale considering the grid operation constraints. Based on this, this paper constructs a market-based electricity optimization model that considers economic benefits and grid operation constraints. Then, a provincial power grid in China is used to simulate and calculate, and the corresponding analysis is given.