The phase transformation and reduction process of vacuum carbothermal reduction ilmenite concentrate at the temperature from 1 000℃ to 1 400℃ were studied by using FactSage, XRD and BSE-EDS. The results showed that reduction temperature promoted the reduction reaction and the nucleation and growth of the metallic iron. The reaction was most intense at the temperature from 1 200℃ to 1 300℃. At 1 350℃, silicon entered the iron phase region. Except for a small amount of Fe₂TiO₄→FeTiO₃ at the initial stage, the reduction process of ilmenite concentrate was basically carried out along the FeTiO₃→FeTi₂O₅→Ti₃O₅→Ti₂O₃. Iron oxides were reduced to metallic iron and aggregated and grown, while titanium oxides changed from high valence to low valence. Finally, the main phases of the reduction were Ti₂O₃ and metallic iron. A solid solution of (Fe, Mg)TiO₃ and M₃O₅ was formed during the reduction process, which restrained the reduction effect of iron.