The three catalysts Mn/Ce-ZrO2, MnCo/Ce-ZrO2, and Mn/Co-Ce-ZrO2 were applied to remove NO in simulated flue gas. Their selective catalytic reduction (SCR) activity and potassium resistance were studied. Catalysts with Co as a modifier of the support exhibited the best SCR activity. The catalyst Mn/Co-Ce-ZrO2 had a larger surface area, higher dispersion of active components, larger amount of surface acid, and better redox characteristics than the other two catalysts, leading to a better SCR activity. X-ray photoelectron spectroscopy results proved the higher surface Mn4+ concentration of K0.3Mn/Co-Ce-ZrO2. Pyridine adsorption analysis suggested that there was still a large amount of Lewis acid in Mn/Co-Ce-ZrO2 even after potassium poisoning, demonstrating the higher resistance of this catalyst to potassium. Mn/Co-Ce-ZrO2 with potassium addition had a relatively stable SCR activity in the presence of H2O and SO2.