The invention belongs to the ferrous metallurgy and environmental protection field, relating to a treatment for offscum, which comprises a converter steelmaking and electric furnace steelmaking technology. The traditional treatment process in current offscum is recycled after dust removal and dust collection, which is a post treatment process. The invention aims to provide a novel process which can reduce dust generation in steelmaking process, and reduces the burning loss of iron and other melt elements in the smelting process. The process comprises mixing a little amount of CO2 gas into oxygen jet flow, reducing the temperature of the flash points region of a molten pool when the mixed gas jet flow is sprayed on the molten pool, controlling the evaporation of iron when the temperature of flash points region is decreased under 2750 DEG C, and reducing dust discharge in steelmaking smelting process, wherein the CO2 content in the mixed gas is controlled within 1-9%, and the content of oxygen is 99-91%. The process is suitable to the technology for the converter steelmaking of 30-300 ton and electric furnace steelmaking of 30-200 ton. The evaporation amount of iron is reduced about 30-70% through adopting the process, and the iron loss which is caused by dust is reduced 5-10kg/t.