The invention discloses a waterproof construction device suitable for a steel structure building. The waterproof construction device comprises a supporting column, wherein universal wheels are arranged at the bottom end of the supporting column; a housing is welded to the upper side of the supporting column; a length sensor is fixedly connected to the surface of the right side of the housing; a switch box is arranged on the part, close to the right side, of the front side of the housing and the upper side of the supporting column; a lock cylinder is arranged on the front surface of the switchbox; a cloth outlet is welded to the edge, close to the right side, of the bottom of the switch box; and a cutting knife is arranged at the bottom of the cloth outlet. By arranging a base layer gelling coating and a surface layer gelling coating, a nozzle is controlled through a PLC, gelling coatings are sprayed to a parapet wall, and polyester cloth is sewn through the arranged sewn polyester cloth to form a seamless waterproof system. The waterproof construction device has the advantages of being super-high in tensile strength, ultraviolet resistance, aging resistance, fatigue resistance, low-temperature flexibility, water-based performance, non-toxic, odorless, non-combustible, non-corrosive and stable in quality, and is the best steel structure roof waterproof system at present.