The utility model relates to an external sensor detecting discharging signal of GIS device, including a bottom open -ended metal -back, be equipped with the antenna that detects the signal that discharges in the metal -back, the signal line of antenna stretches out the metal -back, the outside cover of metal -back is equipped with the metal covering, the metal -back is connected with the benzvalene form insulator, the metal -back is still including establishing shield the ring on the benzvalene form insulator, external sensor detecting discharging signal of GIS device can prevent effectively that external disturbance and jam -proof are effectual.