This is the special machine for assembling the U type and box type beam, it is composed of main machine, roller conveyor, centering device, positioning delvice, hydraulic system and electrical control system. This machine adopt workpiece fixed but machine moving type, hold down workpiece with some pieces and manual welding the workpiece after holding. The characteristic of this machine: finish U type assembling and box type assembling on the same machine, it reduces the cost and saves layout space.