Abstract: MnCeTiO_x catalyst was prepared by the sol-gel method and modified by samarium (Sm) co-doping, which improved its low-temperature selective catalytic reduction (SCR) activity and resistance to SO₂ poisoning. The Sm_nMnCeTiO_x catalysts doped with different samarium-to-manganese ratios were prepared (n=0.06, 0.08, 0.10 and 0.12). The effect of Sm doping on the redox capacity and acid site of MnCeTiO_x catalyst were studied and analyzed by means of BET, XRD (X-ray diffraction), SEM (Scanning electron microscope), NH₃-TPD (Temperature-programmed desorption), H₂-TPR (Temperature process reduction) and XPS (X-ray photoelectron spetroscopy). The catalytic performance was tested by using simulated flue gas, and the best performance of the catalyst was obtained when the mole ratio of Sm to Ti was 0.10. The results show that the doping of Sm can effectively inhibit the crystallization degree of TiO₂, increase the catalyst specific surface area, and make the active elements distribute more uniformly on the catalyst surface. Meanwhile, the doping of Sm significantly improves the surface acidity of the catalyst. It also increases the concentration of surface-adsorbed oxygen, and the mole fraction of Mn⁴⁺ and Ce³⁺. The activity of the catalyst is improved by Sm doping in the temperature range of 120 ℃ to 270 ℃, and the conversion of NO retains above 98% at 180—270 ℃. The doping of Sm effectively inhibits the SO₂ poisoning of the catalyst and reduces the adsorption of SO₂ on the catalyst surface. After a 10 h-SO₂ poisoning test, the catalytic activity decreases by only 2.17%, and partially recovers after SO₂ was quenched, suggesting the anti-sulfur poisoning ability of MnCeTiO_x.