Multiple energy storage units in DC microgrid may encounter some problems during the progress of supplementing or absorbing the power of a system, such as the overcharging and over-discharging problems due to their different initial state of charge (SOC), and the traditional droop control method cannot reasonably allocate load current of the energy storage system in real-time. A new droop control method based on the battery SOC exponent is developed in response to the above problems. The difference from the traditional method is that the new method can change the droop coefficient in real-time according to the change of the SOC exponent so that the battery SOC and the load current reach an equilibrium state. In the paper, the SOC control characteristics are analyzed, and then the reasonable parameters n=2 and p=7 of the SOC exponent control algorithm are selected. The The automatic charging and discharging process under battery charging, discharging, and load fluctuations is simulated on Matlab. It is shown that the proposed method can effectively balance the load current and SOC of the two battery groups. In addition, the voltage fluctuation amplitude is controlled within the allowable range.