Abstract: On the basis of an abnormal case of reclosing line of a 500kV 3/2 switch yard in a converter station, this paper describes the background of the case, and investigates reasons behind this anomalies. Loop checking, insulation testing, replacing plug-ins in the operating relay box and other method was not to eliminate anomalies. By analyzing the coordination of the election phase of closing devices with the control loop of the switch operations relay box, the abnormality was due to the control loop in the phase selection of closing devices that has bypassed open and close relay in the switch operation relay box which led to reclose abnormal discharge atresia. This paper identifies the existence of malfuction in switch reclosing, and potential tripping hazards in similar conditions in the power system. Counter-measures are proposed to be implemented in engineering practice,providing an important reference for improvement for future HVDC system design,commissioning and related devices feature upgrades.