Abstract: According to the metal inert-gas (MIG) welding characteristics of the typical structure of high-speed train,the double elliptical cylinder Gaussian distribution heat source model was proposed, which is suitable for welding of the aluminum alloy sheet. The heat source model based on the shape of weld pool was double elliptical, and the distribution of heat flux was uniform and Gaussian in the thickness and radial,respectively. The welding process was simulated through thermo-mechanical coupling method by finite element method. A comparison between simulation and experimental distribution of the temperature field shows the tendency of evolutionary processes compatibly. The peak value of stress by simulation and experiment are 88.8 MPa and 85 MPa,respectively. The results show that the heat source model can simulate both the temperature and the stress field during the welding process. This method is using to predict welding residual stress and strain for the high-speed train's frame structure and can help to choose appropriate MIG welding parameters of aluminum alloy in the industry.