Abstract: Nitrogen-doped lignin-based activated carbons with different Mn loadings were prepared by impregnation method, aiming to investigate the mechanism of Mn modification on their physicochemical properties and the performance of low-temperature denitrification by NH₃ selective catalytic reduction (NH₃–SCR). The structure and performance of the catalysts were comprehensively analyzed by various characterization means. The results showed that Mn modification significantly reduced the specific surface area and pore volume of the activated carbon, and the diffraction peaks of MnS were detected in the 7% Mn/AC and 9% Mn/AC samples at higher Mn loading. Mn was characterized in the form of Mn²⁺, Mn³⁺ and Mn⁴⁺ forms, and its denitrification efficiency increased with increasing Mn loading, with 5% Mn loading giving the best performance of the catalyst with a denitrification efficiency of 63.4%. It was concluded that Mn³⁺ is the main active substance in NH₃–SCR denitrification process. In addition, the introduction of Mn increased the relative content of O_β, suggesting that O_β plays a key role in the catalyst denitrification process. The NH₃–SCR reaction follows the E–R mechanism. The study provides an important experimental basis for optimizing the preparation of Mn-modified activated carbon and its application in low-temperature denitrification.