The invention provides a mistake preventive locking device of a switchgear. The device comprises an operation door, a controller, a protective plate and a key; an electromagnet is arranged in the operation door, a groove is formed in the bottom of the operation door, and the back side of the operation door is provided with a projection, the electromagnet is communicated with the outside by being connected to the groove via a lead; the controller comprises a shore, a spring, a circular wheel and a cam which are connected successively and then arranged in a vertical hole of the controller, and the vertical hole is positioned blow the groove of the operation door; the controller is further provided with a horizontal hole, a through hole is formed in the center of the cam, and the horizontal hole just faces the through hole so that the key can pass; a hole is arranged under the protective plate and just faces the horizontal hole, and a gap is arranged thereover; and the protective plate ishung on the projection of the operation door via the gap. The mistake preventive locking device of the switchgear is provided with an electroscopic part and a locking switch, whether the internal ofthe switchgear is lively can be detected in double ways, and the safety of operation staff is ensured.