Abstract: Evolution characteristics of ammonium bisulfate (ABS) on the surface of vanadium-titanium catalyst and its influence on catalytic activity were investigated. Physical and chemical properties of the catalyst before and after ABS loading were characterized to obtain the mechanism of the influence of ABS on catalytic activity through methods of XRD, BET, FTIR, TGA, etc. Density functional theory (DFT) calculation was employed to theoretically study the mechanism of different active sites of the catalyst. Denitrification bench experiments were conducted on the ABS-loaded catalyst. Results show that ABS deposition leads to a decrease in the specific surface area of the catalyst. When the ABS content is low, sulfur-containing groups on the catalyst surface primarily exist in the form of SO^2-₄. As the ABS content increases, HSO^-₄ functional groups are generated. The main active sites for the reaction in the catalyst are the Lewis acid sites of vanadium oxide. Sulfide generated by the decomposition of ABS within the catalyst contains Brønsted acid sites which can store NH₃, thus contributes to a certain improvement in catalytic activity. ABS-loaded catalyst exhibits stronger denitrification activity at higher temperature, consistent with DFT calculation results. From a microscopic perspective, trace amount of ABS can enhance catalytic activity.