Abstract: Cracking airway joint of high voltage sulfur hexafluoride circuit breaker in 500 kV substation was analyzed by using macroscopic observation, chemical composition analysis, hardness test, metallographic examination, ammonia fumigation test, scanning electron microscopy and energy spectrum analysis. The experimental results show that the abnormal metallographic structure and the macroscopic segregation of lead elements, the internal stress generated during processing, heat treatment and installation and the existence of corrosive media, which led to the cracking failure of the joint due to stress corrosion.