The invention relates to a cable shielding layer anti-theft alarm device used for a power distribution network. The device comprises a transmitter, a transmitting clamping ring, a receiving clamping ring, a receiver and an alarm, wherein the transmitting clamping ring and the receiving clamping ring are installed outside a cable, the transmitter is connected with the transmitting clamping ring, and the receiving clamping ring is sequentially connected with the receiver and the alarm. The transmitter transmits alternating current signals to the transmitting clamping ring in a certain signal break-make ratio, the alternating current signals are coupled to a shielding layer of the cable through the transmitting clamping ring, the receiving clamping ring receives the signals passing through the shielding layer and then sends the signals to the receiver, the receiver carries out amplification, filtering and A / D conversion processing on the received signals and judges whether the shielding layer of the cable is complete according to the received signals, if the shielding layer of the cable is complete, the signals are displayed, and if the shielding layer of the cable is not complete, the signals are displayed, an alarm signal is sent to the alarm and the alarm sounds an alarm. Compared with the prior art, the device has the advantages of being capable of achieving an anti-theft alarm function and a self-adaptation function, simple in structure, wide in application and the like.