Numerous studies have demonstrated that Na2SO4 can significantly inhibit the reduction of iron oxide in the selective reduction process of laterite nickel ore. FeS generated in the process plays an important role in selective reduction, but the generation process of FeS and its inhibition mechanism on iron reduction are not clear. To figure this out, X-ray diffraction and scanning electron microscopy analyses were conducted to study the roasted ore. The results show that when Na2SO4 is added in the roasting, the FeO content in the roasted ore increases accompanied by the emergence of Fe S phase. Further analysis indicates that Na2S formed by the reaction of Na2SO4 with CO reacts with SiO2 at the FeO surface to generate Fe S and Na2Si2O5. As a result, a thin film forms on the surface of Fe O, hindering the contact between reducing gas and FeO. Therefore, the reduction of iron is depressed, and the FeO content in the roasted ore increases. Numerous studies have demonstrated that Na2SO4 can significantly inhibit the reduction of iron oxide in the selective reduction process of laterite nickel ore. FeS generated in the process plays an important role in selective reduction, but the generation process of FeS and its inhibition mechanism on iron reduction are not clear. To figure this out, X-ray diffraction and scanning electron microscopy analyzes were conducted to study the roasted ore. The results show that when Na2SO4 is added in the roasting, the FeO content in the roasted ore increases accompanied by the emergence of Fe S phase. Further analysis indicates that Na2S formed by the reaction of Na2SO4 with CO reacts with SiO2 at the FeO surface to generate Fe S and Na2Si2O5. As a result, a thin film forms on the surface of Fe O, hindering the contact between reducing gas and FeO. Therefore, the reduction of iron is depressed, and the FeO content in the roasted ore increases.