Abstract: The aluminum alloy plates of 12 mm in thickness in railway vehicles welded by multilayer multi-pass MIG welding was studied by using the elastic-plastic finite element method combined with experimental measurement. By utilizing a more accurate boundary condition simplified method,a unilateral V groove multilayer multi-pass welding finite element model of L-joint was set up to analyze the welding temperature field,residual stress distribution and deformation trend. The results show that the heat accumulating effect of multi-pass welding,welding residual stress and distortion can be accurately simulated by the finite element method. Simultaneously,multilayer MIG welding of L-joint was carried out and the residual stress was measured by the blind-hole method. Simulating results are in good agreements with the actual welding results,which verifies the reasonability of the finite element model.