The invention relates to a drainage plate clamp, is widely applied to work of eliminating heating defects of a drainage plate by a power transmission line ground potential method, and belongs to the technical field of power transmission line live-line maintenance sites. The clamp comprises a clamping part and an insulating operating rod for controlling the clamping part to work, and the clamping part comprises a mother board and a daughter board located below the mother board. The daughter board is connected with the mother board through a daughter board connecting rod. An ejector rod screw sleeve is mounted at the bottom of the mother board, and a fixed column is arranged below the ejector rod screw sleeve. Two penetrating nails are installed on the outer wall of the fixed column, and a rotating ejector rod is connected into the fixed column in a rotating mode. The insulating operating rod comprises a metal head inserted into the screw, and the metal plug is sleeved by an intermediatering, wherein the intermediate ring is sleeved by a locking ring, and an outer pipe I and an outer pipe II are arranged outside the insulating transmission rod in a sleeving mode. The clamp is simplein structure, convenient to install, safe and reliable and wide in application range, improves the live-line work efficiency, and reduces the safety risk of workers.