Abstract: By finite element method, the relationships between the fracture parameter of CTOD and the mismatch parameter of welded joints are studied on the condition of the mixed-Mode crack of the welded joints which contain a single-edge crack on the fusion line. Considering the distribution of strain-stress field at the tip of a crack, the parameters of CTOD components are decomposed. Moveover, the displacement-component of Mode Ⅰand of ModeⅡ are calculated for the different load levels. In the end, the calculated results are analysed and the engineering treatments methods of the fracture parameter of CTOD of welded joints are also proposed.