In the track of metro vehicle manufacturing process,stainless steel body side wall beam adopting column structure has the characteristics of large size,welding parts,how to predict and control the welding deformation,to ensure that the design size is an urgent research topic in rail vehicle manufacturing plant. Firstly,the long-term tracking of a side wall unit after welding flatness were found,the welding deformation of the side wall of the unit;secondly,the establishment of a local finite element model,the simulation of welding deformation using the finite element software,analyze the reason of side wall unit deformation trend,and puts forward the applied reverse before welding two kinds of beam deformation and increase the process control measures;finally the feasibility of this method is proved,the control unit of the factory wall stainless steel side welding deformation has important significance.