Hybrid energy storage，consisting of super capacitor and battery，has been widely applied to smooth wind power fluctuation because it can overcome the disadvantage of single energy storage technology.To ensure reliable charging and discharging performance of hybrid energy storage and fully take advantage of the characteristic of fast reaction of super capacitors and large capacity batteries，this paper proposes a wind power smoothing method using hybrid energy storage system based on hierarchical optimization of state of charge（SOC）.This method adopts two-layer distributed control structure，including optimizing control layer and coordinated control layer.In the optimizing control layer，the target power of dynamic adjustment energy storage system is calculated according to the performance requirements of wind power smoothing and the current SOC of the system.In coordinated control layer，power distribution strategy is decided according to the SOC and charging and discharging characteristics of the energy storage devices and the target power calculated by the optimizing control layer，achieving fast tracking of reference power input.Simulation results indicate that the method can not only mitigate the wind power fluctuation，but also improve the charging and discharging performance of the hybrid energy system.The SOC of two energy storage devices is optimized and over charging and discharging of energy storage devices is avoided.