The part through surface cracks exist widely in practical welded structure, and the investigation of the elastic plastic
fracture mechanics parameters (eg.
J integral) of this three dimensional mechanical heterogeneity is not enough. In this paper, the J integral of surface cracks in overmatched weldment with different
matching ratios has been investigated by using direct evaluation method. The influences of matching ratio of joints on the crack driving force ( J integral, crack mouth opening displacement CMOD) and strain distributions along the contour have been discussed in detail. The results indicate that the comprehensive effect of crack position and the matching ratio of welded joint dominate the distribution of strain. With the increasing of load, the obvious strain concentration may be produced in the parent metal zone close to weld. Moreover, with the decreasing of the matching ratio, the degree of the strain concentration grows, the deformation of weld metal decreases to a certain extent, and the crack driving force increases.