Iron-based catalysts are nontoxic and have outstanding medium-temperature activity, which are considered as potential catalysts for the selective catalytic reduction of NO_x with NH₃ (NH₃-SCR). In this work, Fe (0.2)-W (0.05)-Ti catalyst prepared by deposition–precipitation exhibited over 90% NO_x conversion within the range of 280–420 °C and excellent resistance to SO₂ or H₂O. The excellent catalytic performance was due to the high proportion of Fe²⁺/(Fe²⁺ + Fe³⁺) and O_ads/(O_ads + O_lat) ratio and abundant surface acid sites. However, the catalyst lost part low-temperature catalytic performance after hydrothermal aging at 670 °C for 64 h. The surface area, proportion of Fe²⁺/(Fe²⁺ + Fe³⁺) and O_ads/(O_ads + O_lat) decreased significantly after aged. As a result, the lack of sufficiently active site to produce NO₂ resulted in the significant decrease for NO_x conversion at low-temperature section. Simultaneously, the decline of the surface acidity, especially the strong acid, meant that the adsorption capacity of the catalyst under high temperature weakened and the NO conversion corresponding declined.