Abstract: The existing firing control cannot generate the firing pulses accurately under AC faults, which will increase the risk of subsequent commutation failure of LCC-HVDC system. Therefore, the firing control system was analyzed in detail by establishing a small signal model, and an improved firing control method was proposed. In this method, the phase of commutation voltage is tracked quickly by the CDSC-PLL, and improve the trigger mode according to the rapid detection of AC faults. In this way, the actual firing angle can change quickly and accurately according to the firing angle order, which is more conducive to the precise regulation of the HVDC control system. Finally, the improved firing control was tested in the CIGRE HVDC benchmark model. The simulation results show that it can effectively reduce the probability of subsequent commutation failure and improve the recovery performance of HVDC system.