Distributed energy storage system plays an important role in maintaining voltage stability of DC microgrid. The traditional virtual DC motor control strategy makes the converter have the external characteristics of DC motor and provides additional inertia and damping support, but it cannot realize power distribution in parallel system. In addition, the drop-down control strategy can realize dynamic power distribution according to the State of Charge (SOC) of each energy storage unit, but it cannot provide additional inertia and damping for the system. To solve this problem, a parallel control method of virtual DC machine (VDCM) with dynamic power balance function was proposed, taking two buck-boost converters of energy storage devices as an example. In this paper, the power distribution principle of VDCM parallel system based on P-U droop control is analyzed firstly, and an integral link is introduced in droop control to compensate the drop of bus voltage. Secondly, the dynamic balance of output power between energy storage units is realized by introducing SOC unbalance degree. Finally, the simulation results show that the proposed method can restrain the fluctuation and sag of bus voltage better than the traditional VDCM control and droop control, and can realize the dynamic power balance between energy storage units.