Currently, selective catalytic reduction (SCR) of NO x with NH3 in the presence of SO2 by using vanadium-free catalysts is still an important issue for the removal of NO x for stationary sources. Developing high-performance catalysts for NO x reduction in the presence of SO2 is a significant challenge. In this work, a series of Fe2O3-promoted halloysite-supported CeO2-WO3 catalysts were synthesized by a molten salt treatment followed by the impregnation method and demonstrated improved NO x reduction in the presence of SO2. The obtained catalyst exhibits superior catalytic activity, high N2 selectivity over a wide temperature range from 270 to 420 °C, and excellent sulfur-poisoning resistance. It has been demonstrated that the Fe2O3-promoted halloysite-supported CeO2-WO3 catalyst increased the ratio of Ce3+ and the amount of surface oxygen vacancies and enhanced the interaction between active components. Moreover, the SCR reaction mechanism of the obtained catalyst was studied using in situ diffuse reflectance infrared Fourier transform spectroscopy. It can be inferred that the number of Brønsted acid sites is significantly increased, and more active species could be produced by Fe2O3 promotion. Furthermore, in the presence of SO2, the Fe2O3-promoted halloysite-supported CeO2-WO3 catalyst can effectively prevent the irreversible bonding of SO2 with the active components, making the catalyst exhibit desirable sulfur resistance. The work paves the way for the development of high-performance SCR catalysts with improved NO x reduction in the presence of SO2.