Electro-polishing process for the welding nickel-based alloy of AP1000 upper head CRDM nozzle was studied. The improvement on the surface roughness and residual surface stress were investigated. The results show that the current density should be controlled in the range of 0 . 3 ~ 0 . 5 A / cm²and the polishing time should be within 2 ~ 5 min. The residual stress tests in surface demonstrate that tensile stress is remarkably decreased, and even pressing stress is induced by the electropolishing process, which may restrain the occurrence of stress-corrosion cracking in the welding nickel-based alloy.