Extinction angle control is one of the main control strategies for commutation failure mitigation in an HVDC, but the problem of too slow response and control precision still cannot be solved effectively based on the current research on measured and predictive extinction angle control. Thus, an improved extinction angle control method to mitigate subsequent commutation failure is proposed. First, the influence of voltage harmonics on the commutation process of the HVDC system is analyzed, and the prediction method of extinction angle considering voltage harmonics is proposed. Then the predictive value of the subsequent commutation process is introduced into the original control logic of the system to improve extinction angle control. Finally, the proposed control method is simulated and verified based on PSCAD/EMTDC standard test system. The simulation results show that the method can improve the response speed and control precision of the extinction angle control, and thus can effectively mitigate the subsequent commutation failure in HVDC system.