Abstract: Based on specific conditions of welding metallurgy technology concept of dissimilar steels, according to actual application of welding conditions and verification results of experimental research and aiming at repair welding of large medium carbon cast steel parts, a practical technology combination scheme of optimizing welding materials and processes was put forward. Special welding wires (Cr20Ni-10Mn7Si-ZG) for Mn, Ni austenitic high alloy steel that could significantly improve weldability (resistance of cold crack and hot crack) were used to avoid pre-welding and post-welding heat treatment (complete cold welding) and obtain excellent mechanical properties of weld. By prefabricating welded structural reinforcement of shell structure in the groove, heat field distribution in welding thermal cycle and stress condition of welded structure were improved, and fatigue resistance of welded structure was improved. The prefabricated three-dimensional rigid skeleton system constructed by built-in steel web indiscriminatingly offset shrinkage stress perpendicular to groove wall generated by condensation of welding filling metal through rigid support without gaps, which could maximize control of welding deformation and reduce crack growth rate.