This paper presented an equivalent CTOD concept, based on the local approach, to transfer fracture toughness results to fracture performance evaluation of structural components. The equivalent CTOD was defined by the CTOD in the toughness specimen which gave a compatible Weibull stress between the toughness specimen and structural component. Fracture toughness determination by the equivalent CTOD concept leads to a reasonable toughness requirement to meet a design condition for the structural component, while the conventional procedure requires excessive fracture toughness to a large extent. The equivalent CTOD methodology is useful for evaluation of strength mis-match effect on the required toughness of welds. The undermatch condition needs a larger toughness for the weld metal (WM) than the overmatch condition. Nevertheless, using a weld metal with high workhardenability, the required WM toughness in the undermatch condition can be lowered to a level in the match condition. By contrast, the required toughness for the heat affected zone (HAZ) in the undermatch condition is less than that in the overmatch condition. This was explained in terms of the local stress field in the HAZ : the stress level is elevated and relaxed by the overmatch condition and the undermatch conditions, respectively. A discussion was followed as to the allowable range of strength mis-matching to meet the required deformability of structural components.