Abstract: Corrosion resistance of carbon steel 20 and stainless steel 304 in FGD waste water of different pH values was studied using electrochemical method, while the variation law of gaseous chlorine volatilization and the inhibiting effects of different pH value conditioning agents on the chlorine volatilization were explored during evaporation of the waste water under different pH value conditions. Results show that when the pH value of waste water lies in 9-10, both the general corrosion and crevice corrosion of the two steels would be relatively slight, with less volatilization of chlorine. Meanwhile Ca(OH)₂ can inhibit chlorine volatilization effectively, this is beneficial to the solid phase transition of salts from FGD waste water.