Abstract: In wet zinc smelting process, iron slag generated by hematite process has high iron content, uniform particle size, and stable thermodynamics, which have evident advantages. However, impurities are present in hematite slag, including jarosite, basic ferric sulfate, adsorptive salts, and small amounts of iron carbonate and iron silicate, that limit its comprehensive recovery and utilization. In view of these impurities in hematite slag, in this study, iron oxide red was prepared using a high-temperature hydrothermal method. The effects of different acidity levels, temperatures, preparation times, and liquid–solid ratios on the contents of iron, zinc, and sulfur were studied, as were the removal rates of zinc and sulfur and dissolution rate of iron. The experimental results show that the iron content in the iron oxide red products increases from 58.66% to 66.83% at following parameters: pH 1, temperature 220 ℃, preparation time 3 h, liquid–solid ratio 6∶1, and rotation speed 400 r·min⁻¹. The iron content of the ferrous minerals increases from 94.05% to 97.79%, sulfur content decreases from 2.96% to 0.82%, and zinc content decreases from 1.03% to 0.18%. As determined by X-ray diffraction, compared with hematite slag, the peak value of the iron oxide signal in the iron oxide red products is higher and that of the miscellaneous peak is lower. Scanning electron microscopy analysis/energy dispersive analysis of X-rays show that the amounts of sulfate and other impurities on the surface of the iron oxide red products are significantly reduced after high-temperature hydrothermal treatment. However, the morphologies and sizes of the hematite slag and red iron oxide product particles do not change. After the experimental treatment, the iron oxide red products are determined to meet the national standard: iron oxide red content grade C, water soluble substance and water-soluble chloride and sulfate content type III, sieve residue type 2, 105 ℃ volatile type V₂, source type a standard.