The utility model relates to a lock-up control circuit between a motor power supply and a control power supply of a knife switch mechanism. A relay is connected to motor power supply bus of the knife switch mechanism. The contact terminal of the relay is connected between control power supply bus of the knife switch mechanism and a control power supply bus power supply. When the motor power supply circuit of the knife switch is powered off, power supply of a motor control circuit is cut off so that self hold of the control circuit is inactivated. When the motor power supply circuit is powered on again, misoperation of the motor is prevented. Compared with a product in the prior art, only one relay is used in the lock-up control circuit so that cost is substantially reduced.