To evaluate the corrosion mechanism of Fe-2.25Cr-1.6W(wt.%) steels were corroded between 600 and 800 ℃ for up to 200 h in Na2SO4. Corrosion rates increased progressively as the corrosion time increased. The formed outer scale grew into the air by the salt during corrosion, which facilitated outward diffusion of Fe2+ ions. The inner mixed layer grew by the inward diffusion of oxygen ions. The Fe-2.25Cr-1.6W(wt.%) steel corroded little fast, forming thick scales that consisted primarily of an outer and middle Fe-O layer and an inner (Fe, Cr, O)-mixed layer. At the interface of the outer and inner scales, voids developed and cracking occurred. Fe-2.25Cr-1.6W(wt.%) steel had a small amount of Cr, which cannot decreased the scaling rate and the adhesion of scale.