Selective catalytic reduction technology is the most widely used method for industrial flue gas denitration. However, the preparation of the catalyst is complicated and the preparation cost is high. A new type of catalyst for selective catalytic reduction of nitrogen oxides was prepared by roasting, sulfuric acid and sulfuric acidroasting treatment of steelmaking sludge from iron and steel enterprises. By using specific surface area analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF) and temperature-programmed desorption of ammonia (NH3-TPD) and other characterization methods, the changes in the physical and chemical properties of the steelmaking sludge catalyst before and after the treatment were analyzed and studied. The results show that the main active components of the catalyst are Fe, Mn, V, and Ti. The roasting modification has a certain improvement effect on the catalyst activity and can convert the Fe3O4 in the catalyst into α-Fe2O3 with better denitration activity. The sulfuric acid modified catalyst has excellent catalytic activity and the denitration efficiency can reach 88.5% at 300°C. It changes the surface morphology of the catalyst, reduces the crystal grain size, and generates a large number of sulfate species. This provides more acidic sites on the catalyst surface, thereby promoting the improvement of catalytic performance. It provides a basis for the development of low-cost denitration catalysts and promotes clean production in the metallurgical industry in this research.