Abstract: Battery energy storage system（BESS） has become a key component of the power grid due to its advantages of improving the accommodation capacity of renewable energy.However,the inconsistency of batteries caused by production and usage processes is a critical factor affecting the capacity and lifespan of energy storage systems.Based on the topology of highvoltage DC cascaded H-bridge converter-battery energy storage system（CHBC-BESS）,a hierarchical control strategy is adopted.Based on the first-level control for a voltage mode and a power mode,a state of charge（SOC） self-equalizing control strategy with adaptive control parameters is proposed to solve the problem of battery SOC unequalizing.The strategy considers the battery SOC deviation,the voltage levels of each module capacitor,the margin in DC system voltage control,and the upper and lower limits of the output modulation ratio.The equalizing coefficient is calculated in real time.Experimental results verify that the proposed strategy can achieve fast self-equalizing and high equalizing efficiency under the working conditions of large SOC deviation and the extreme working conditions of full-power charge-discharge switching.