Abstract: Mn-Fe/FA(N) and Mn-Fe/FA catalysts were synthesized by using the ultrasonic-assisted precipitation method. These catalysts consisted of fly ash (as the carrier), Fe (ferric nitrate as the precursor) and Mn (manganese nitrate or potassium permanganate as the precursor). The NH₃-SCR reactions were conducted in a specially designed fixed-bed reactor. The de-NO_x and the resistance (SO₂ and H₂O) mechanism of catalysts were analyzed by X-ray photoelectron spectroscopy (XPS), NH₃-temperature programmed desorption (NH₃-TPD) and H₂-temperature programmed reduction (H₂-TPR). The results showed that the NO_x conversion of Mn-Fe/FA was significantly higher than that of Mn-Fe/FA(N). The Mn-Fe/FA catalyst exhibited a wider operating temperature range (70~200℃). Moreover, Mn-Fe/FA catalyst maintained the initial NO_x conversion (99%) for 4h in the H₂O (5 or 10%) at 200℃. In the presence of SO₂ and H₂O at 200℃, Mn-Fe/FA was able to maintain over 75% NO_x conversion after 4h. KMnO₄, as a source of Mn in Mn-Fe/FA, promoted the redox properties of the corresponding catalyst and increased the concentrations of active metal ions (Mn⁴⁺, Fe³⁺) and chemically adsorbed oxygen. It was found that using KMnO₄ as a source of Mn can inhibit the formation of metal sulfates.