Abstract: Taking the upper Ω sealing structure of CRDM in M310 nuclear power unit as the research object, the crack control of ERNiCrFe-7A surfacing layer on convex and special-shaped structure was studied. The influence of arc extinction voltage and decay time on crater crack was studied. The influence of welding current, arc voltage, welding speed and other welding parameters on ductility dip cracking (DDC) was studied. The results showed that crater crack and ductility dip cracking were the main crack forms. Crater crack could be prevented by strengthening welding protection effect, controlling decay time and adopting reasonable welding sequence. DDC generated by ERNiCrFe-7A during surfacing of convex and special-shaped structure could be avoided by appropriate welding heat input.