Abstract: Numerical simulation of TIG welding of thin plate by thermo-elastic finite element method (FEM) was conducted. By double ellipsoid thermal source,thermophysical parameters varying with temperature were used to compare the influence of heat conductivity,specific heat capacity and density on the welding residual stress. The result shows that the drop of the heat conductivity will lead to the increment of the welding residual stress,and the longitudinal residual stress transits from the double hump to the single one; the falling of the specific heat capacity can also reduce the welding residual stress,which can greatly be affected by the difference of density between aluminum alloy and mild steel,and the double hump of the longitudinal residual stress will disappear with the density increasing. Then the three thermo-physical parameters,heat conductivity,specific heat capacity and density,make the longitudinal welding residual stress of aluminum alloy is lower than its yield limit and appears double hump effect near the weld seal. The welding longitudinal residual stress for the flat plates of 2024-T4 aluminum alloy is simulated by using cutting pieces stress relieving method. The simulation results are well accordant with the test ones,which prove the validity of the simulation results.