The invention relates to a lockout device for preventing the misoperation of an active current pressing plate under the condition of current. The device comprises an alternating current induction sampling circuit, and is characterized in that the alternating current induction sampling circuit is connected with a soft switch; the soft switch is connected with a power amplification circuit and a flicker alarm circuit; and the power amplification circuit is connected with a voice alarm circuit and a forced lockout device. The lockout device can prompt and give an alarm when current passes through a differential protection alternating current loop to fulfill the aims of preventing switching operation and preventing the misoperation accidents of CT connection straps in the test operation.