At present, when an asymmetric fault occurs on the inverter side of an HVDC transmission system, prediction is not that effective using the minimum turn-off angle discrimination method, which only considers the voltage factor. To solve this problem, based on the analysis of the mechanism and the influencing factors of commutation failure, it is shown that both the rise of DC current and the reduction of AC voltage can make the turn-off angle decrease. Therefore, by decoupling the DC current and the AC voltage, an expression of the inverter side turn-off angle only related to the changing rate of voltage is obtained. This is taken as the criterion. This criterion can be used to calculate the critical voltage changing rate that leads to commutation failure based on the operational parameters of the DC line and the inverter side. In the process of commutation, when the changing rate of the system voltage is less than that of the critical voltage, the system has a greater risk of commutation failure. A CIGRE HVDC model is built based on the PSCAD/EMTDC software, and the simulation experiments of single phase ground fault with different transition resistance are carried out. The test results verify the validity of the proposed method. This work is supported by National Natural Science Foundation of China (No. 51877185).