Abstract: Electrochemical corrosion tests and immersion corrosion tests were conducted on the base metal and overlay welding specimen of corrosion-resistant alloy NS334 in concentration 6 wt%-24 wt%FeCl₃ solution. The corrosion morphology,corrosion weight loss rate and corrosion mechanism were studied using SEM, LSCM and other methods. The results indicate that the electrochemical corrosion rate of NS334 base material and overlay welding specimen is positively correlated with solution concentration. When the concentration of FeCl₃ exceeds 18 wt%, the corrosion resistance rapidly decreases, and the corrosion weight loss rate of the base material increases from 0.02 g/（m²·h） to 0.05 g/（m²·h）, the corrosion weight loss rate of the overlay welding specimen increases from 0.025 g/（m²·h） to 0.11 g/（m²·h）. The strengthening effect of twinning small angle grain boundary on corrosion resistance of the base material and the weakening effect of refined grain on corrosion resistance jointly result in the base material having better corrosion resistance than the overlay welding specimen. Chloride ion corrosion mainly occurs along grain boundaries and secondary dendrites and extends inward.