Abstract: The influence of mis-match ratio and total width of cover pass on distributions of welding residual stresses are studied by finite element method for the application of undermatching butt joint of high strength steel.Although the weld strength mismatch effects are confined to a small region in the weld, all critical zone of fatigue failure such as weld toe and root of weld are located in this region.At weld toe, the magnitude of the longitudinal residual stresses increases and the magnitude of transverse residual stress decreases with increasing mis-match ratio.The magnitudes of the longitudinal residual stresses and transverse residual stress increase less with the increasing of total width of cover pass, but the position of peak value changes.The peak value of transverse residual stress of generic undermatching butt joints is located at base metal, but that of equal load-carrying undermatching butt joint corresponding to the increasing of total width of cover pass is located at weld toe.