The invention relates to the technical field of a ground wire device in power system transformer substation, in particular to a ground wire automatic monitoring device, which comprises a central processing unit (CPU), a line communication module, an output relay, a warning lamp relay, a voice module, a first coupler, a second coupler, a loudspeaker, a net gate switch and a grounding terminal switch for ground wire signal collection, wherein the grounding terminal switch consists of a bolt, a spring, two nylon sleeves, a fixing electrode and a movable electrode; the fixing electrode and the movable electrode are provided with signal wire wiring holes; the end of the bolt for sheathing the movable electrode is meshed with a nut; and the nylon sleeve forms a concave shape to perform the insulation function. The fixing electrode and the movable electrode are in the shape of a groove for meshing with the nylon sleeves. When the ground wire is put on the movable electrode, the spring is pressed to make the movable electrode in contact with the fixing electrode, and the electrical signal is conducted. After the ground wire is disassembled, the movable electrode and the fixing electrode are separated and the electrical signal is disconnected, thus the functions of electrical signal outputting after the ground wire is connected and electrical signal disappearance after the ground wire is disassembled is achieved. The invention can prevent the accident caused by switching on with ground wire.