Because of the intermittent nature of renewable energy sources, energy storage units are widely used in islanded DC microgrids. To protect the energy storage units and prevent overcharging or deep discharging, it is necessary to implement balanced control of the state of charge (SOC) of the units. However, the differences in line impedance and capacity of each energy storage unit will affect the balance of the SOC. To address this issue, a SOC balancing control strategy for energy storage units based on a consensus algorithm and adaptive droop control is proposed. First, by defining the current proportional coefficients, a functional relationship between the droop coefficients of each energy storage unit and the SOC is established, achieving adaptive SOC balance of the energy storage units. The stability of the system is proved by the Routh criterion. Secondly, the proposed control strategy is compared with other control methods in the literature, and the impact of four different working conditions on SOC balance is considered. Finally, simulation analysis is carried out using Matlab/Simulink, verifying the effectiveness of the proposed control strategy.