This invention relates to the electric power system error-proof closedown technique field. The air-proof earthing device of the error-proof closedown system includes: an upper lock body, a down lock body, wherein the outer of the lock body has two coding heads and two lock holes; the two sides of the inner lock are arranged with left and right operating poles separately, one end the operating poles is arranged with the operating pole spring, and the middle of the two operating poles has the lock slot, the down part of the lock slot has a directional pin, the pin can slide on the slipway that corresponds to the upper lock body, the inner side of the two inspecting block have an inspecting replacement spring separately; the down part of the left and right operating poles is arranged with the left and right spring bolts, left and right locking pins, the inner side of the left and right spring bolts all connect with the upper lock body by the spring bolt spring, the down part of the left and right spring bolts have a lock button separately; the left and right locking pins have a locking pin spring separately, one end of the locking pin spring is locked in the middle of the locking pin, the other is locked on the upper lock body; the middle of the upper lock body has an earthing line slot. The device in this invention improves system's safety.