The effects of the welding mechanical heterogeneity on the damage evolution of notched round-bar tensile specimens were investigated numerically using a fully coupled elastic-plastic damage finite element method. Some parameters reflecting the welding mechanical heterogeneity such as strength mismatching, rupture strain and weld metal width were taken into account to study their effects on the damage evolution of the weld metal. The calculation results show that the damage evolution of the weld metal is affected strongly by the welding mechanical heterogeneity. The damage evolution of the weld metal becomes larger with the decrease of both the rupture strain and yielding stress of the base metal. The effects of the mechanical properties of the base metal on the damage evolution of the weld metal decreases with the increase of the weld metal width.