Abstract: The abnormal CO content of a sulfur hexafluoride circuit breaker was found in the test of detecting SF6 gas decomposition products by electrochemical sensor method. Combined with other test conditions, the operation of the circuit breaker was comprehensively analyzed, and the abnormal CO content was determined to be caused by the interference of H2 on the CO sensor when detecting SF6 gas decomposition products by electrochemical sensor method. The measurement result is inaccurate. In order to verify the analysis, the SF6 gas of the circuit breaker was sampled and analyzed by gas chromatography. The result showed that the gas sample contained high H2 and the CO content was normal, which verified the accuracy of the analysis.