Abstract: The roof of 350 km/h EMU has severe deformation after welding,the maximum amount of post-welding deformation is 12 mm. In the welding process,the adjustment of the welding sequence can reduce the post-welding deformation effectively. First welding the reverse side,then the front side and first the middle welds,then the edge welds can obtain smaller amount of post-welding deformation. Under this condition,the bending direction is consistent with the direction of the roof after welding and the trimming time is the shortest. The application of the fixture and the prefabrication of reverse deformation in the welding can reduce the amount of post-welding deformation further. When the amount of reverse deformation reaches 7 mm,the amount of post-welding deformation can be controlled within 3 mm.