<p>Herein, iron was doped to improve the medium–low-temperature NH₃-SCR activity of COS + CS₂ gas-phase sulfating CeO₂-S catalyst, and it presented a synergistic promotional effect with COS + CS₂ sulfation on the catalytic performance of CeO₂ catalyst. The results indicated that Fe doping promoted the formation of Fe–Ce solid solution, which decreased the crystallinity and inhibited the growth up of cubic fluorite CeO₂ crystals. Meanwhile, this solid solution in Ce_0.5Fe_0.5O_<i>x</i> catalyst could be partially destroyed by COS + CS₂ sulfation, and Ce_0.5Fe_0.5O_<i>x</i>-S presented larger CeO₂ crystals than CeO₂-S with a large number of iron sulfate formed in it. Furthermore, the formed cerium-iron solid solution enriched the defective sites of both CeO₂-S and CeO₂ catalysts, but the sulfation of COS + CS₂ and Fe doping all promoted the formation of oxygen vacancy in the CeO₂ catalyst, despite the detrimental effect of sulfation on the cerium-iron solid solution. However, the sulfation of COS + CS₂ could not inhibit the promoted redox cycle of Fe²⁺ + Ce⁴⁺ ↔ Fe³⁺ + Ce³⁺ in Ce_0.5Fe_0.5O_<i>x</i> catalyst, and Ce_0.5Fe_0.5O_<i>x</i>-S presented larger surface molar ratios of both Fe³⁺/(Fe³⁺ + Fe²⁺) and Ce³⁺/(Ce³⁺ + Ce⁴⁺). Fe doping depressed the surface sulfation of cubic fluorite CeO₂, but promoted the formation of iron sulfate with lower thermal stability. Furthermore, Fe doping and COS + CS₂ sulfation presented a promotional effect on the redox property of CeO₂ catalyst, and the latter decreased the inhibition of Fe doping on the acid sites of catalyst. This study reveals the unique synergy between Fe doping and organic sulfur sulfation, providing new insight into developing high-performance Ce-based SCR catalyst.</p>