The invention discloses a steel structure welding and clamping device for a building. The device comprises a protection cover and two supporting vertical plates, a driving mechanism and a lifting mechanism are mounted in the protection cover, a supporting plate is mounted on the top of the protection cover, a strip hole is formed in the supporting plate, the two supporting vertical plates penetrate through the strip hole, extend into the protection cover, and are matched with the driving mechanism, the lifting mechanism is mounted above the driving mechanism and is mounted between the two supporting vertical plates, the two ends of the lifting mechanism are mounted on the two supporting vertical plates, a clamping mechanism is mounted on the inner side of each supporting vertical plate, asteel structure can be clamped, welding precision is ensured, under the effect of the driving mechanism, the steel structure can be driven to rotate, a worker can conveniently weld the steel structure, the lifting mechanism can lift the steel structure required to be clamped to the same horizontal plane of the clamping mechanism, the clamping mechanism can conveniently clamp the steel structure, and the work efficiency can be improved.