Abstract: Based on commercial V₂O₅-WO₃/TiO₂ catalyst, two methods to simulate CaSO₄ poisoning were designed, and the physico-chemical properties of fresh and poisoned catalysts were investigated by BET specific surface area measurement, X-ray diffraction (XRD), H₂ temperature-programmed reduction (H₂-TPR), scanning electron microscope (SEM) and in-situ diffuse reflectance infrared spectrometry (in situ DRIFTS). Meanwhile, the catalytic performance for selective catalytic reduction of NO with NH₃(NH₃-SCR) in a fixed bed was also explored comparatively. SEM results show that CaSO₄ plugs the small hole (pore width smaller than 2.7 nm) and big hole (pore width bigger than 17.8 nm), causing the loss of surface area and pore volume. CaSO₄ could weaken the intensity of both Br∅nsted acid Sites and Lewis acid sites, particularly the active centers of Br∅nsted acid sites, which hinders the absorption of NH₃ and reduces the redox abilities.