To reduce the probability of both commutation failure and continuous commutation failure in HVDC power transmission system, the main reasons causing commutation failure are analyzed, which include the voltage amplitude drop of commutation bus, direct current uprush and commutating voltage zero-cross phase shift. An optimal control strategy in which the extinction angle setting value can be adjusted dynamically considering zero-cross phase shift of commutation bus voltage at the inverter side and delayed trigger is allocated at the rectifier side is proposed. The influence of the optimal control strategy on system operating parameters is also analyzed. Based on the CIGRE benchmark model of HVDC, the proposed control strategy is developed in PSCAD/EMTDC. Simulation results show that the proposed optimal control strategy, to some extent, has the ability to mitigate the commutation failure and continuous commutation failure under single-phase and three-phase grounding fault conditions. Thus, the fault recovery performances of HVDC can be effectively improved.