In order to study the initiation and propagation of weld structure cracks,four different weld toe chamfer weld cross joint models were established by using abaqus software. The extended finite element method（XFEM）was used without pre-set cracks. The type is set to the plane stress state and the plane strain state,respectively,and then the crack initiation expansion simulation is performed. The results show that the crack is more likely to sprout and expand under the plane strain state,and the weld toe chamfer has an influence on the crack initiation position and the extension path.