VMoTi catalyst was prepared separately by impregnation method (IM) and sol-gel method, and the alkali metal K poisoning of the catalyst was simulated. The X-ray diffraction, BET specific surface area test, NH₃-temperature programmed desorption (TPD), H₂-temperature programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS) methods were used to analyze the physical and chemical properties of the VMoTi catalyst, and the reaction and deactivation mechanisms of the vanadium-titanium-based catalyst were discussed. The results show that compared with the catalyst prepared by IM, i.e., VMoTi (IM) catalyst, the catalyst prepared by the sol-gel method, i.e., VMoTi (Sol-gel) catalyst, has a smaller grain size, a larger specific surface area and pore volume, a larger amount of surface acid, a stronger redox capacity, and a higher content of V⁴⁺, Mo⁴⁺, and surface active oxygen. Therefore, VMoTi (Sol-gel) catalyst shows a good denitration efficiency stabilized at ~100% in the temperature range of 180~320 °C. The addition of potassium (alkali metal) leads to catalyst poisoning, and the poisoning effect of the catalysts prepared by different methods is different. The K salt deposition has a great influence on the denitration efficiency of the VMoTi (IM) catalyst. The VMoTi (Sol-gel) catalyst has good resistance to K poisoning. Through the characterization of the catalyst, it is found that K salt weakens the interaction between the active ingredient and the carrier, enhances the intensity of the diffraction peak of anatase TiO₂, and reduces the acidity and redox of the catalyst surface. At the same time, the content of chemical adsorption of oxygen and active metals, such as V⁴⁺ and Mo⁴⁺, decreases. These factors are the main reasons of the catalyst inactivity.