In view of the flaw of voltage imbalance due to differences in loss exhibited by H bridge module on the DC side of the cascade static synchronous compensator (STATCOM), and based on the notion of hierarchical control and energy exchange, an improved interphase voltage equalization control strategy has thus been proposed. Based on the modulation wave obtained from the global voltage regulation control, an error component parallel to the direction of the active current has been superimposed, thus shifting the tiny angle of the trigger angle, which enables a reasonable allocation of the energy between each phase and each H bridge module, and thus achieving the purpose of balancing the DC side voltage of H bridge modules. The simulation results show that the control strategy can effectively balance the inter-phase and phase voltage on the DC side of STATCOM.