In order to reduce the adverse impact of location and capacity of charging station in distribution network, this paper considers the load fluctuation and voltage offset of the distribution network to build a optimal planning model for the location and size of electric vehicle (EV) charging stations. First of all, the cost of investment operator and the cost of user are comprehensively considered to construct the optimization model that minimizes the sum of investment and construction costs, operation and maintenance costs, and user costs of charging stations. Then, under the distribution network constraints, the evaluation model is built for the distribution network with the smallest loss, the smallest load fluctuation rate, and the smallest voltage offset indicator. Genetic algorithm is combined with Voronoi diagram to obtain the site and capacity of the charging station and select the comprehensive optimal scheme with the least impact on the distribution network and the total cost. Finally, the transportation network and power grid information are combined in the planned area. The simulation results verify the rationality and effectiveness of the model.