Abstract: Based on the thermo-mechanical coupling analysis with nonlinear commercial software MSC.Marc, the welding deformation of large-scale hollow extruded aluminum alloy high-speed rail floor was simulated under present technological conditions.A moving double-ellipsoid heat source was employed in the model for MIG welding process, and the dynamic mechanical and thermal-physical properties of the 6N01 aluminum alloy and ER5356 filler metal were adopted to improve the calculation precision.The results show that the as-welded deformation of rail floor joined by seven pieces of aluminum alloy extrusion profiles was V-type angular distortion in the thickness direction, and the maximum deflection was 14.86 mm in the horizontal direction.Moreover, an optimized welding sequence was put forward, which was symmetrically welding from the lateral to the center.With the same deformation tendency, the deflection of the optimized rail floor weld was reduced to 78.6% of that under the present scheme.For large-scale and complex structures, gravity should be seriously considered for control of welding deformation.