The invention discloses a dismounting device for a large steel moulding plate in double-layer board wall construction. The dismounting device comprises an I-shaped framework, supporting feet, lifting rings, a long lead screw mechanism, a bearing and a steering wheel, wherein first reinforcing parts are respectively arranged on the upper top surface and the lower top surface of the I-shaped framework, second reinforcing parts are respectively arranged on the inner corners of the I-shaped framework, the supporting feet are arranged at four feet of the I-shaped framework, the lifting rings are positioned at the tops of the supporting feet, the long lead screw mechanism is positioned on the I-shaped framework through the bearing, and the steering wheel is positioned on the long lead screw mechanism. The dismounting device solves the problem that form board construction is difficult to be carried out on a small-cavity double-layer board wall. The dismounting device is matched with a large steel mould, is simple to dismount, is reliable in connection, is not prone to deforming and can be utilized repeatedly.