Abstract: The penetration of distributed power sources such as photovoltaic and wind power in the flexible distribution network is increasing. In order to reduce the adverse impact of intermittent output on the power system, the energy storage system is introduced. However, due to the differences in battery characteristics, hardware parameter configuration and other aspects of each energy storage unit, the effective service life of the energy storage unit will be shortened. Aiming at the problem of SoC imbalance and output voltage fluctuation of distributed energy storage unit, this paper proposes an SoC equalization control method based on fuzzy theory. Taking the state of charge of each energy storage unit and the voltage deviation of the energy storage port as the input of fuzzy control, the reference voltage superposition value of each energy storage unit is obtained. This indirectly controls the DC/DC converter to change the input/output current of the energy storage unit, thus realizing the charge and discharge control of the energy storage unit. Finally, the remaining power is balanced and the output voltage of the energy storage system is stable. In the PSCAD simulation software, the fuzzy theory based SoC balancing control strategy for flexible distribution network is simulated and verified, which proves the effectiveness of the proposed method.