An electric power warning board locking device is provided with a U-shaped frame. The bottom wall of the U-shaped frame is a vertically arranged flat plate. Two sides of the flat plate are respectively and fixedly provided with a rim. A plurality of hanging rods are arranged between the two rims at intervals. One ends of the hanging rods are fixed on the bottom wall flat plate horizontally, and the other ends of the hanging rods stretch out a notch of the U-shaped frame. The outer ends of the two rims are respectively provided with a U-shaped clamping ring, and a locking rod is arranged on the two U-shaped clamping rings horizontally. Active infrared intrusion detector switches are arranged on ring bodies of the U-shaped clamping rings. The locking device is designed directing at the current situation that an existing electric power department warning board is disordered in management. On one hand, the locking rod is used for blocking a warning board out-moving port in the hanging rods, and on the other hand, the locking rod is used for controlling the active infrared intrusion detector switches. When the locking rod is displaced, the active infrared intrusion detector switches emit control signals to realize wireless alarming, and therefore the purpose of monitoring a waning board in real time is achieved.