When the AC system of the receiving end fails, the DC transmission system based on the grid commutator has a problem of commutation failure, which will cause the DC transmission power to be interrupted. The excess reactive power at the sending end will cause the AC system to overvoltage. In turn, it is possible to cause new energy equipment such as wind turbines to be disconnected from the network. Therefore, a control strategy is proposed to suppress over-voltage at the transmitting end during commutation failure. The specific strategy is to quickly input bypass switch of the inverter side when the commutation failure occurs and calculate the DC current command value during the fault according to the reactive power consumption before the fault. The strategy can maintain a certain DC current in the mode of the active power interruption, thereby ensuring the converter valve can normally commutate and have a certain reactive power consumption to avoid the overvoltage problem of AC grid. The simulation results verify the effectiveness of the control strategy which can be applied to both strong and weak AC systems with different short-circuit ratios.