Abstract: It is feasible to enhance the grid-connecting reliability of wind power generation by smoothing the wind power fluctuation with the help of battery energy storage system. Considering the adjustment of state of charge (SOC) in energy storage system, a control strategy of smoothing wind power fluctuation based on parabola regular variable filtering time constant was proposed. Through parabola regular variable filtering time constant algorithm the target value of grid-connected active power of energy storage system was obtained, and through such links as restriction of change rate, correction SOC and power amplitude limiting the actual power output of battery energy storage system was determined and issued to stored energy converter to perform charging and discharging of the battery. Thus, the wind power fluctuation could be smoothed and the SOC could be maintained within the safe range. Simulation results show that the proposed control strategy is feasible and effective.