Abstract Through the analysis of disintegration a tripping fault of the 500kV hybrid gas insulated switchgear, confirmed the cause of fault is due to internal defects of disconnecting switch's insulating tension pole. The internal defects gradually deteriorated in the operating process, and the flashover happened. Then in process of reclosing, thebreakdown products and shielded cap of moving contact dropped on the level basin insulation, it caused the flashover of insulator, later the isolator broke down. In all these cases, we put forward recommendations to improve device reliability.