Abstract: For large volume defects found in the manufacturing process of cylinder of supercritical steam turbine,according to two welding repair cases, the feasibility and safety of the cylinder repair using nickel-based welding rod were studied. The results show that using nickel based alloy electrode, SMAW with small specification parameters, and interlayer hammer to eliminate stress, dehydrogenation heat treatment after welding if necessary, it is feasible, safety and reliable for the repair of large defects in Cr Mo steel and martensitic heat resistant steel cylinder casting used in supercritical turbine.