Abstract: The high voltage circuit breaker is an important equipment in the power system, which is responsible for the dual tasks of controlling and protecting the circuit, and its performance is one of the important factors to determine whether the power system can supply power safely. This paper mainly discusses the abnormal situation of a nuclear power plant VD4 circuit breaker refusing to operate, detects and analyzes the failure of the high voltage circuit breaker, and finds out the root cause of the failure.