In order to meet the requirement of weight reduction,rail vehicles are increasingly using aluminum alloys. The lap joint is one of the common forms of rail vehicles and it is of great significance to optimize the welding process,reduce the welding deformation and improve the service life of rail vehicles by exploring the welding residual stress distribution and deformation regularities. The MIG welding temperature fields,stress fields and deformation of 2.2 mm and 3 mm lap joints of 6005 A-T6 aluminum alloy are simulated by using thermo-elastic-plastic finite element method. The simulation results are compared with the experimental ones. It is shown that they are in good agreement,which verifies the accuracy of the established finite element model. The welding residual stress of aluminum alloy lap joint is mainly distributed in the weld and heat affected zone,the change in the thickness direction is not obvious,on the whole,the distribution of residual stresses is asymmetric. Welding deformation mainly appears at the edge of the lower plate parallel,the maximum deformation reaches 2.6 mm,and in the longitudinal direction of the plate also produces concave downward deformation.