Abstract: The three-dimensional numerical simulation on welding stress in pulsed TIG welded joint of aluminum alloy thin plate was performed by means of thermal-elastic-plastic FEM technology.The welding residual stress was measured by Mathar method.The results show that the welding stress generates and develops rapidly during welding process.The welding stress achieves the value of stable state before long heating end.The large instantaneous longitudinal and transversal compress stresses exist in the front and by both sides of heat source.The longitudinal residual stress in the welding center is less than the yield strength of base metal, and the maximum longitudinal residual stress at 10 mm away from weld center is up to the yield strength of base metal, and the width of tensile stress zone is quite wide, and the compressive residual stress away from weld is quite large.Therefore, the buckling occurs easily in thin aluminum alloy plate during and afterwelding.The numerical simulation results of the longitudinal residual welding stress in the cross section of thin aluminum alloy plate is compatible with the measuring result.