In the past,argon arc welding was used for 100% carbon steel road passenger cars,φ（Ar）80%+φ（CO2）80% gas shielded arc welding,using ER44-8 filler material. The operator’s skill requirements were high,and the heat generated during welding was large. It is easy to cause deformation of the workpiece and poor appearance quality,so it is more and more difficult to meet the user’s requirements for welding quality. The application of the spot welding technology in the carbon steel EMU reduces the output of the welding heat and the deformation of the welding process,especially its successful application in the side wall steel structure,which greatly improves the flatness requirements and surface quality of the side wall.