The invention discloses an automatic wire clamp for a portable short-circuit ground wire. The automatic wire clamp is easy and convenient to operate and wide in application range. The automatic wire clamp comprises an operating rod, a static bracket, a connecting shaft, a transmission rack, a pawl, a pawl spring and a movable wire clamp, wherein the transmission rack is connected to the front end of the connecting shaft; the pawl can be meshed with a tooth tip on the outer surface of the connecting shaft; the pawl spring is arranged between the static bracket and the pawl; and the movable wire clamp is connected to the static bracket. A fixed wire clamp is arranged on one side of the front part of the static bracket. An intermediate gear meshed with the transmission rack is also arranged in an inner cavity of the static bracket. The movable wire clamp comprises a middle opening part corresponding to the fixed wire clamp and a mounting part movably arranged on the static bracket. A rack meshed with the intermediate gear is arranged on the outer end face of the mounting part. The front end of the operating rod is connected with the connecting shaft through a limiting cam. A rib is arranged on the surface of an inner cavity on the rear part of the static bracket to stop the limiting cam continuing rotating when the high surface of the limiting cam rotates to the position of the rib. A resetting spring is connected between the fixed wire clamp and the movable wire clamp.