Abstract: Commutation failure is one of the common failures in high voltage direct current（HVDC） transmission systems using line-commutated converters（LCCs）. The occurrence of commutation failures will cause DC power fluctuations and even DC blockage, threatening the safe and stable operation of the power grid. In order to focus on the key issues of commutation failure and reduce the probability of commutation failure, this paper summarizes the related research on commutation failure of HVDC transmission systems. First, the mechanism of commutation failure is analyzed from both the device and the system aspects. Then,according to the sequence of occurrence of commutation failures, the commutation failures are divided into two cases: the first commutation failure and the subsequent commutation failure. The influence factors and restraining measures of different commutation failures are analyzed. Finally, based on the existing research, the unsolved problems in the field of commutation failure are pointed out.