Abstract: Due to differences in physical and chemical properties of dissimilar steels, interface distribution and crack failure mechanism of welded joints are different from those of the same steel during welding. Starting from failure mechanism of dissimilar steel welded joints, softening and embrittlement phenomenon of fusion zone caused by carbon migration were introduced in this paper, the essential reason for the decrease of mechanical properties in welding process was analyzed, formation mechanism of Type-II grain boundary and white bright layer was explained in detail, and formation mechanism and suppression measures of dissimilar steel welded cracks under high stress level were analyzed. The essential reasons for failure of dissimilar steel welded joints were systematically discussed, which provided theoretical guidance for in-depth study and engineering application of failure mechanism of dissimilar steel welded joints, and put forward solutions to common failure problems of dissimilar steel welded joints.Highlights: (1) Based on characteristics of weld transition zone, research progress of failure mechanism of dissimilar steel welded joints was analyzed. It was proposed that key measures to improve performance of welded joints were to inhibit formation of Type-II grain boundary in transition zone and reduce width of white bright layer. Mechanism of softening and embrittlement of dissimilar steel welded joints caused by carbon migration was clarified by discussing carbon migration in dissimilar steel welding.(2) It was proposed that quantitative control of distribution of welding thermal stress and residual stress based on precise application of cold source was an effective measure to improve welding crack failure of dissimilar steels.