Abstract: By using elasto-plastic finit element calculation and three point bending test, the influence of strength matching and ciack depth on fracture properties are investigated. The main points of this paper are the influence of strength matching and crack depth on the plastic zone, boundary value of depth and shallow crack behaviour, fraaure resistance properties, crack tip opening displacement CTOD, and J-integral in loading proasses for welded joint specimens. The results show that the plastic zone becomes large when the crack depth turns short, and the fracture toughness turns high, the plastic zone of overmatch joint specimens are larger than that of undermatched joint specimens in loading processed at the same CTOD value, because the plastic zone of overmatched joint specimens are extend to the base metal but that of undermatched joint specimens are restricted in the welded seam. Overmatched joint specimens may more easily show the fracture behaviour of shallow crack than undermatched joint specimens, while the two sorts of joint specimens have the same crack length. Therefore, the frac-ture-resistent capability of overmatched weld is better than that of undermatched weld.