The event of abnormal noise of 220 kV gas insulated substation（GIS）circuit breaker in operation at one 500 kV substation is introduced.The detection process is analyzed

the circuit breaker is returned to the manufacturer and the current rise test is performed.The circuit breaker generates abnormal noise when the current rising up to a certain level.It is found by the disassembly that the bonding between the oil-less bearing and the intermediate contact seat in the interrupter of the circuit breaker is not tight.It is concluded through the test that the appearance dimension of the oil-less bearing exceeds the specification and untight bonding with the intermediate contact seat are the direct reason of the event.The current rise diagnostic test of circuit breaker in the same batch is carried out and the equipment with similar faults is replaced.The corresponding suggestions and measures are proposed in accordance with cause of the fault.