Elastic-plastic finite element analysis was performed to study the welded joints with a semi-elliptical crack. This research includes the effects of crack depth, strength mismatch ratio, and weld width on the crack driving force J-integral and the constraint parameter A 2 at the crack tip. A two-parameter J-A 2 fracture criterion based on the present results of crack tip stress field in the welded joints was established. The corresponding failure assessment diagrams were investigated in detail, from which the reliability and safety margin of the welded structures were discussed.