Steel slag tailings are the main solid waste in metallurgical industry, with the production of 15%~20% of crude steel. The utilization ratio is quite low and only reaches 10% of steel slag tailings production due to limited technology. Meanwhile, steel slag tailings are disposed in direct stacking and landfill in general since the management system is not perfect, which pollutes land source, underground water source and air quality. Recycling of solid waste is one important method to achieve sustainable development of resources. The main chemical compositions are CaO, SiO2, Al2O3, MgO, Fe2O3, MnO, f-CaO, etc. In the face of the above problems, the development of low price and superior performance of activated carbon mixed with steel slag composite material has become not only one of main methods to achieve the high value-added utilization of metallurgical solid waste and the sustainable development of resources, but also one of main methods to achieve the great reduction of the production cost of modified activated carbon and improve economic benefits. In this paper, activated carbon and steel slag were studied firstly, and activated carbon mixed with steel slag composite material for sintering flue gas of desulfurization and denitration was prepared by metal oxides contained in the steel slag were modified to treat the activated carbon, and desulfurization and denitration performance of activated carbon mixed with steel slag composite material was tested by setting up the experimental reaction device. Chemical component of steel slag was characterized and analyzed by X-ray fluorescence spectrometer (XRF), pore structure of activated carbon mixed with steel slag composite material was characterized and analyzed by specific surface area and pore size distribution analyzer (BET), composition structure of steel slag was characterized and analyzed by Fourier transform infrared spectrometer (FTIR) and microstructure of activated carbon mixed with steel slag composite material was characterized and analyzed by scanning electron microscope (SEM), so as to reveal the mechanism of preparing activated carbon mixed with steel slag composite material from activated carbon and steel slag, and the degradation mechanism of desulfurization and denitration in sintering flue gas by activated carbon mixed with steel slag composite material. The results show that the activated carbon mixed with steel slag composite material (steel slag is layer pouring slag from electric furnace, mass ratio of steel slag to activated carbon is 2:4 and fineness of steel slag and activated carbon is 400 mesh) has good properties of desulfurization and denitration and reasonable economy with desulfurization efficiency of 100% and denitration efficiency of 58%. The porous structure of activated carbon mixed with steel slag composite material adsorbed SO2 and NO, and Fe2O3 and MnO2 in steel slag promote the catalytic reduction reaction of activated carbon functional groups to improve the properties of desulfurization and denitration, where adsorption is the leading and prerequisite, and catalytic reduction reaction is auxiliary and synergistic. It aims to provide a new way for the utilization of high value-added steel slag, and achieve the target of waste management waste and waste to increase efficiency in iron and steel enterprise.