Abstract: The installation of battery energy storage on a wind farm is an effective way to smooth the wind power fluctuation and improve the controllability of wind power. In this paper, we proposed a control method for smoothing wind power fluctuation with multiple energy storage unit output levels, in which the real-time output capacity of multiple storage units is fully taken into consideration. Besides, the utilization of energy, the switch number of charge/discharge, the range and difference of state of charge are decreased while ensuring the power smoothing target. Firstly, we analyzed the effect of the filtering time constant on the smoothing wind power and influence of power allocation method on the SOC change of each unit, respectively. Secondly, the short-term forecast is introduced. The optimal solution of filtering time constant and minimum power command are calculated by the filtering time constant optimization model. Moreover, the relationship between the output level of each storage unit and the power command is analyzed, and the power command is allocated according to the hierarchical composite power. Finally, the effectiveness of the proposed method is verified in a case study by using actual wind power data from a wind farm in Hunan province.