The disordered planning and unreasonable allocation of electric vehicle charging stations have a serious impact on the safty，stability and economy of the distribution network operation．To solve this problem, this paper constructs an optimal planning model of electric vehicle charging stations based on the voltage stability index of distribution network．The model not only could balance the construction investment of charging stations，the economic operation of distribution system and the quality of power supply，but also take full account of the demand and convenience of the electric vehicle charging．The improved adaptive particle swarm optimization (APSO) algorithm with fast speed and high accuracy is adopted to solve the nolinear optimization problem with multiple constraints. Finally, the simulation results based on IEEE33bus system show the effectiveness of the proposed method.