Abstract: In order to ensure the safe operation of GIS, the disruptive discharge faults on site operation of potential transformer (PT) for GIS was classified and analyzed. The production, field installation and operation conditions of each type of PT disruptive discharge fault was studied, the results show that the main factors of PT disruptive discharge fault were oil pollution, foreign matters in iron core, microscale water content, impurities and ferroresonance. And in order to improve the operational reliability of PT products, the corresponding process control measures were formulated.