Abstract: With the rapid process of industrialization, the emission of nitrogen oxides (NO_x) has become increasingly prominent and has become a key issue that urgently needs to be addressed in the field of environmental protection. The excessive emission of NO_x not only causes acid rain, exacerbates urban haze and other environmental problems, but also poses an undeniable threat to human health. Therefore, it is particularly important to develop and apply efficient NO_x reduction technologies, which have significant implications for improving air quality and protecting the ecological environment. Among numerous technologies, ammonia selective catalytic reduction (NH₃-SCR) technology is highly favored due to its excellent performance and practicality, and has become the most widely used NO_x removal technology at present. The core of this technology lies in the development of catalysts that are both cost-effective, highly effective, and possess strong anti poisoning properties. This study aims to address the problems of poor denitrification performance, narrow reaction temperature window, and poor anti poisoning performance of existing commercial catalysts for low-temperature flue gas treatment. A Mn₇-Cu₃-Nb_x/BCN catalyst with good low-temperature catalytic activity was prepared by microwave-assisted impregnation method through Nb doping modification. The NH₃-SCR test results showed that the Mn₇-Cu₃-Nb_0.05/BCN catalyst with a Nb content of 0.05% exhibited the best SCR catalytic activity. The catalyst had a NO conversion rate of not less than 94% in the temperature range of 150−275 ℃, and the N₂ selectivity was also improved. The experimental results of anti water and anti sulfur poisoning showed that the Nb doped modified catalyst Mn₇-Cu₃-Nb_0.05/BCN also had good anti poisoning performance. After introducing 1.0×10⁻⁴ SO₂ and 5% H₂O for 14.75 hours, its NO conversion rate can still be stably maintained at over 75%. The enhancement mechanism of Nb doped modification on the low-temperature SCR denitrification performance of Mn₇-Cu₃/BCN catalyst was investigated in detail using various characterization methods such as SEM, XRD, XPS, NH₃-TPD, NO-TPD, and in-situ infrared diffuse reflectance spectroscopy (in-situ DRIFT). The results indicated that Nb doping modification can effectively suppress the crystallization of CuO and Cu species on the surface of Mn₇-Cu₃/BCN catalyst, further promoting the uniform dispersion of active components. Meanwhile, the doping of Nb effectively increased the concentration of Mn⁴⁺and O_α species, promoting the oxidation of more NO to NO₂ and facilitating the “Fast-SCR” reaction process. In addition, In addition, Nb doping modification could enhance the surface acidity of the catalyst, promote the adsorption and activation of NH₃ and NO, accelerate the formation of more beneficial intermediates such as -NH₂ and nitrate, and effectively improve the overall reaction rate of SCR denitrification reaction. In addition, Nb doping modification could effectively reduce the poisoning effect of SO₂, and this excellent anti sulfur poisoning performance was mainly attributed to the effective suppression of sulfate formation on the catalyst surface by the introduction of Nb, especially the metal sulfate MnSO₄. This study provides important scientific basis for a deeper understanding of the impact mechanism of Nb doping modification, and provides useful exploration and reference for the development of low-temperature flue gas denitrification technology.