Abstract: In coal-fired power plants, the flue gas after wet desulphurization still contains strong corrosive substances such as SO₃, HCl, HF and so on. Higher requirements are put forward for the corrosion resistance of the chimney even though the content is not that high. The wet electrostatic precipitator installed after the desulphurization has certain removal effect for the corrosive substances. In order to study the removal efficiency of wet electrostatic precipitator, samples were taken from the inlet and outlet flue gas of a metal plate type wet precipitator in a 330 MW unit of a power plant to detect the concentration of SO₃, HCl and HF. It is concluded that the removal efficiency of the wet electrostatic precipitator for the strong corrosive acid gases was 45%, 85% and 65%, respectively. The results show that the wet electrostatic precipitator can effectively remove the corrosive gas in the flue gas and reduce its concentration at the inlet of the chimney, and therefore the corrosion rate of chimney can be slowed down.