Abstract: In order to explore the physical properties of magnetite in the roasted copper slag in the molten state, a melt oxidation roasting experiment was conducted on the copper slag in a CO/CO₂ atmosphere. The effects were investigated of CaO addition and calcination temperature on the transition process of Fe₂SiO₄ to Fe₃O₄ in the slag, and the migration and enrichment of Fe₃O₄. The addition of CaO promotes the conversion of Fe₂SiO₄ to Fe₃O₄ in the slag and the migration and enrichment of Fe₃O₄, and the properly selected roasting temperature can maximize the migration and enrichment of Fe₃O₄. Finally, it was found that the addition of CaO was 25 % of the mass of the copper slag, the calcination temperature was 1 300 ℃, the holding time was 2 h, and the volume of CO₂ and CO was 190:10. The Fe₂SiO₄ in the copper slag had basically completed the conversion to Fe₃O₄ and its migration and enrichment degree was better.