Welding residual stresses in thin structures may cause buckling distort ions. By using the finite element method (FEM) based on the inherent strain and applying the nonlinearity function in ANSYS, this paper investigated mode ling o f sidewall welded and structure distortion prediction for a railway freight car . A simulation model was built. After being verified by the experimental results , An FEA model was adopted to perform the welding simulations of orthogonal desi gn as well as the main effect plot analysis. The rule was discovered in terms of design variables and process parameters impacting on the welding distortion. Wh ich included that the thickness of side sheet metal was the key factor and the w elding speed, voltage, current in the next place, and the span between the two sidebeams was positive correlation with the welding distortion, but depending on the position in the whole wall, and the cap shape beam structure had a better antidistortion capacity compared with the slotshape one, and the horizontal con necting had a little advantage compared with the vertical one. The research outc ome above strongly supports the optimization design and manufacturing for side wall of freight cars and establishment of design criterion of flatness error as well.