China's power supply is mainly based on thermal power generation. In the future, large-scale electric vehicles purchasing electricity from large grids cannot meet the need for low-carbon travel of electric vehicles with high charging costs. In order to effectively improve this problem, this paper proposes a new strategy for wind-PV-pumped storage multiple electric fields to participate in the current market bidding and power supply for electric vehicles by signing grid contracts with State Grid Corporation of China. First, load modeling is performed for electric vehicles with different charging methods. Then, an optimized electricity purchasing strategy is established with the goal of minimizing the cost of purchasing electricity for electric vehicle users. Finally, a purchasing strategy result is obtained through an improved particle swarm algorithm containing randomly mutated particles. The simulation results show that compared with traditional and non-bidding power purchase strategies, the charging cost of electric vehicle users of each type is reduced, compared with the existing power purchase strategy. At the same time, it will help promote using of renewable power plants and electric vehicles. This work is supported by the National Natural Science Foundation of China (No. 51607031) and Jilin Science and Technology Innovation Development Project (No. 20190104138).