Islanded DC microgrids generally need to be configured with multiple energy storage units to ensure the stability of the system. To realize state-of-charge (SOC) equalization of multiple energy storage units during charging and discharging, and to prevent overcharging and over-discharging from accelerating the aging, an improved SOC stabilization and equalization control strategy is proposed. First, the power finger function nested inverse tangent function is used to construct the relationship between droop coefficient and SOC, and the parameters of acceleration factor and convergence factor in the droop coefficient are reasonably designed to make the SOC reach the equilibrium state quickly and realize adaptive control. After that, the influence of the control parameters of this strategy on system stability is discussed. Finally, simulation results verify that the proposed control strategy can better achieve fast and stable equalization of SOC, accurate current distribution and smaller bus voltage deviation with better stability under normal charging and discharging, load or PV power fluctuation, and with different rated capacities of energy storage units.