Abstract: When an asymmetric fault occurs on the inverter side, the leading firing angle of the inverter will be affected by two factors: the asymmetrical commutation voltage and the DC control adjustment. The commutation voltage of each valve is calculated using the symmetrical component method, and the results show that the asymmetry of the commutating voltage will cause a periodic fluctuation of the leading firing angle. In the meanwhile, it is found that the firing angle order contains second harmonic components after analyzing the HVDC control system output characteristics. Combining the effects of two factors, the leading firing angle exhibits periodic fluctuation characteristics, which can easily cause continuous commutation failure in the recovery process of DC system.According to the hysteresis control theory, a control strategy to suppress continuous commutation failure by reducing the leading firing angle fluctuation range was proposed. Simulation experiments were conducted in PSCAD/EMTDC to verify the proposed mechanism and effectiveness of the control strategy.The results confirm that during the recovery process after a commutation failure, the periodic fluctuation of leading firing angle is the primary cause of continuous commutation failure in the HVDC system, and the proposed control strategy has the ability to mitigate the continuous commutation failure under single-phase ground fault conditions.