Abstract: During the operation of the 3AT3EI circuit breaker, there may be signals such as "pressure prohibition reclosing" and "nitrogen leakage". If not dealt with in a timely manner, it will affect the normal operation of the circuit breaker. This article takes a 500 kV outgoing circuit breaker as an example, analyzes the hydraulic mechanism control circuit based on on-site fault phenomena, determines that the cause of signal transmission is hydraulic oil pressure contact adhesion, and summarizes the fault causes and corresponding treatment measures.