The invention discloses a steel plate surface polishing device for a steel structure building. The steel plate surface polishing device comprises a fixing plate, a discharging hole, supporting legs, afirst motor, a conveying belt, magnet blocks, a storage shell, a steel plate, a grinding roller, a fixed frame, a second motor, a water pipe, nozzles, a supporting plate, a water storage tank, a material pouring plate, a connecting frame, rollers, a connecting plate and a metal scrap filter screen. A steel plate surface polishing device for the steel structure building is simple in structure, novel in design and capable of realizing automatic conveying of the polished steel plate, and meanwhile, the stable fixation of the conveyed steel plate is guaranteed, the polishing roller conveniently polish and polish the steel plate surface to be polished, the grinding and polishing efficiency of the steel plate is improved, the grinding roller and the surface of the polished steel plate can be washed in the grinding process, and the surfaces of the grinding roller and the steel plate are guaranteed to be clean; and in addition, the steel plate surface polishing device conveniently blanks theground steel plate, is convenient to use by workers, facilitates washing and filtering of washed waste liquid, and is convenient to process by the workers, and suitable for popularization and use.