Abstract: A tri-material model was proposed to investigate the effects of HAZ on the limit loads of mismatched welded joint.Some assumptions of materials and geometries of welded joint were given in the finite element limit analysis.The finite element analysis were carried out on the welded joint with a series of configurations of different materials properties,different widths of HAZ and different groove angles.The results show a significant influence of mismatched materials,especially the HAZ of welded joint,on the limit load ratio.The results also illustrate the changing trend of the limit load ratio with the various groove angles and widths of the HAZ of the mismatched welded joint.Numerical simulation results show that the limit load of mismatched welded joint is determined by the yield strength of HAZ.The regression equation in this paper can calculate the limit loads of mismatched welded joint.