The energy storage system makes it possible for randomly fluctuated wind power to participate pre-determined power dispatching.However，both the adaptability of power dispatching decision and the economy of wind power system operation including storage system must be taken into account in the capacity planning.An optimization model for determining energy storage capacity is proposed，based on the reference value of wind farm output power suitable for power dispatching operation program.The optimization model aims to minimize the total cost of energy storage infrastructure and operation including loss of wind energy and storage system.The model can fully guarantee the economy of wind-storage system and minimize the probability of power fluctuation of wind farm in the power dispatching operation program，and achieve a stable and effective coordination between the wind power dispatch and main network dispatch.An improved particle swarm optimization（PSO）algorithm is used to calculate and analyze the example system，and the model is proved to be effective.