Because the upper and under bridge arm voltage of each phases are inconformity with each other based on MMC-HVDC, resulting in the internal circulation of converter. Circulation will cause each phase converter arm current distortion, so it is important to suppress the circulation. The usual method for inhibition circulation inhibits the internal circulation of converter under the normal operation condition. Firstly, it analyzes the method of inhibiting circulation under normal circumstances. Then, it focuses on the effects of unbalanced current under fault condition on the internal circulation and DC current through the AC system single-phase ground fault analysis and designs the additional controller to improve the traditional inhibition circulation strategy under fault conditions. Finally, it verifies the feasibility of theoretical analysis and improvement measures through the PSCAD/EMTDC simulation experiments.