Abstract: Electrochemical corrosion behavior of FV520B stainless steel in 3.5wt% NaCl solution and in 3.5wt% NaCl solutions containing CO₂, H₂S and CO₂+H₂S, respectively, was studied by potentiodynamic polarization and electrochemical impedance spectroscopy. The results show that the open circuit potential of the test steel shifted to the negative direction, the polarization resistance decreased and the corrosion resistance became worse. The polarization curves of the test steel in four corrosive media showed anodic dissolution characteristics. In the 3.5wt%NaCl and 3.5wt%NaCl+CO₂ solutions, the corrosion was dominated by anodic reaction; in the 3.5wt%NaCl+H₂S solution, the corrosion was dominated by cathodic reaction; the corrosion was dominated by the anodic and cathodic reaction when H₂S and CO₂ coexisted in the 3.5wt%NaCl solution.