Abstract: Based on the thermo-mechanical coupling analysis of FEM,the joining process of high speed rail floor was studied,which was welded by seven pieces of large-scale hollow extruded shape of aluminum alloy.To enhance the calculation precision,the mechanical and thermal-physical properties of the aluminum alloy and its filler metal were tested between room temperature and their melting points,moreover,the moving double-ellipsoid heat source was employed to simulate the metal-inert gas welding.The measured as-welded deflection data of ten real rail floors at the production site was highly coincident with the numerical simulation results.The results proved that,the thermo-mechanical coupling analysis and the dynamic material properties were two essential factors in the high precision simulation of high speed rail floor,which could lay a digital workplace for the improvement of the current process and further development of the new-type assembly.