Carbonthermic method was adopted to reduce the iron in the form of fayalite in copper slag to metal iron in this study. The reduction was undertaken under the conditions of roasting reduction at 1423 K for 4 h with specified parameters that the ratio of copper slag versus anthracite was 2∶1, and that the ratio of calcium carbonate to silicon dioxide was 1.43∶1. It was demonstrated that the metallization efficiency of iron could reach 88.26%. Moreover it was showed that the reduction process of fayalite by carbon could be routed as: Fe2SiO4(or 2FeO·SiO2)→ FeO + 2CaO·SiO2→ Fe. In addition it was proved that the combination ability between calcium positive ion and silicon oxygen anion was bigger than that between iron positive ion and silicon oxygen anion. As a result，SiO2 compacted in fayalite could decompose easily and could combine with CaO at the reaction temperature, therefore FeO could exist with a form of freedom state which could be reduce easily by carbon or monocarbon produced in carbonthermic method.