In order to take advantage the energy storage system in maintain the power balance of microgrid system, an improved state of charge(SOC) based dynamic droop control method with self-compensation for energy storage systems was proposed in this paper. As the droop coefficient of traditional droop control is too large, which lead to bus voltage deviation, and the fixed droop coefficient is applied to charge and discharge control of energy storage system, which would cause overcharge and over-discharge of battery. For this issue,a new dynamic droop coefficient is designed based on the system power balance relationship, and the output power of the energy storage system is proportional to their respective SOC values. In addition，the voltage compensation algorithm was deduced to eliminate the bus voltage deviation caused by droop control. Finally, an improved droop control of the energy storage system is obtained. The above method reduces the control complexity compared to the conventional secondary control. For this purpose, multiple groups of small-capacity energy storage systems are used to balance distributed power (DG) and load power to control bus voltage stability. To analyse the stability of the three power grid modes: power shortage, system power excess, and partial power system fault removal in the microgrid system. Finally, the proposed control structure was verified by Matlab / Simulink simulation. The simulation results show that in three different modes of the microgrid, the energy of the energy storage system can always be distributed proportionally according to the SOC value, and finally satisfy the SOC balance and power balance. Compared with traditional droop control, the DC bus voltage fluctuation of microgrid is smaller and the precision of the power distribution is higher.