Abstract: The sending and receiving ends of the high voltage direct current (HVDC) have electrical coupling and control coordination relationships. The sending end fault can cause the commutation failure of the receiving end by affecting the operation of the receiving end system through system control logic, parameter transfer and so on. However, the interaction and mechanism of this process are still unclear. In view of this, starting from the sending AC system, the whole response process of the receiving end to the sending AC fault was discussed, finding that the main cause of commutation failure was the voltage drop of AC bus voltage at receiving end caused by excessive reactive power consumption during fault recovery process. Furthermore, the influence of AC system fault on commutation failure risk was analyzed in detail under the imbalance reactive power state of the rectifier AC system, and the analysis indicated that insufficient reactive power compensation would reduce the commutation failure probability, while excess reactive power compensation would increase the commutation failure probability. Finally, based on the CIGRE DC transmission standard test system, the correctness of the conclusions under different fault conditions were verified through a lot of simulations.