Abstract: A 110 kV circuit breaker in a 110 kV substation has a gas leakage problem for a long time. After SF₆ is filled without poweroff, the maintenance worker searched the fault with gas leakage detection technology. Then they found the cause of gas leakage of the circuit breaker and put forward defect treatment scheme, which completely solved the gas leakage problem of the circuit breaker, avoided the occurrence of circuit breaker refusal accident caused by low air pressure locking, and ensured the safe and stable operation of the equipment.