This paper proposes an optimal energy storage units (ESUs) operation strategy with efficiency improvement and state of charge (SoC) balance by considering converter characters and network loss. First, the optimal power-sharing ratio considering minimized power loss of paralleled ESUs is obtained with the Lagrange Multiplier Method. Second, the optimal power-sharing ratio with SoC balance of ESUs is obtained. On the basis of it, the optimal operation strategy of paralleled ESUs with efficiency improvement and SoC balance is proposed. The power-sharing ratio of ESUs changes actively according to system operation status. Under the proposed control strategy, the difference in the SoC of each paralleled energy storage unit can be controlled within a desired range. Meanwhile, the system efficiency can be improved. In that case, the system's overall performance can be improved. The effectiveness of the proposed strategy is verified through the real-time simulation with RT-Lab. The proposed control strategy can enhance ESU operation performance with efficiency improvement and SoC balance.