Abstract: For structural integrity assessment of welded joints is difficult to assess, the failure assessment diagram prediction method for the critical stress of heat affected zone crack initiation of welded joints is established by using the "tri-material" assumption model of mismatched welded joints. Based on the finite element analysis of ABAQUS software, the crack initiation in the heat affected zone of welded joint is studied. Results indicated that over-matching weld promoted the HAZ crack initiation in mismatched welded joints. HAZ strength softening promoted the HAZ crack initiation in mismatched welded joints. When M_W<1, M_H<1, with the increase of heat affected zone width, it promoted the HAZ crack initiation, M_H>1, with the decrease of heat affected zone width, it promoted the HAZ crack initiation. When M_W>1, whether HAZ strength softening or hardening, with the increase of heat affected zone width, they promoted the HAZ crack initiation.