Abstract: Commutation failure is one of the most common faults in high-voltage direct current (HVDC) transmission system, which will shorten life span of the converter valves and cause over-voltage of weak AC system at inverter-side, and it will also result in HVDC blocking fault and other serious problems in severe conditions. The bipolar blocking of 500 kV Linfeng HVDC system caused by continuous commutation failures on August 19 2013 is described as a case here. Through detail discussing the protection configuration in commutation failure and the protection action process of this fault, the deep reason of this fault is summarized, and recommendations and improvements are put forward, whose feasibility is verified. In the end, the related suggestions for real operation of power grid are presented, which provides reference for project design and operation management for HVDC project.