Abstract: In the present study, the formed crystal phases in TiO_x-SiO₂-MgO system under various oxygen partial pressure at different temperature ranging from 1873 K to 1473 K were characterized. The oxygen partial pressure was controlled by H₂/CO₂. In the H₂/CO₂ atmosphere (volume ratio of H₂ to CO₂ is 300 and 150), the corresponding oxygen partial pressure at 1873 K, 1673 K and 1473 K ranged from 1.22×10^-8~2.18×10^-12Pa and 4.92×10^-8~8.79×10^-12Pa respectively. The crystal phase was identified by combining X-ray diffraction with energy dispersive spectrometer analysis (EDS). Comparing to the previous study by Wang Daya et al, the result demonstrated that when the oxygen partial pressure is relatively high (volume ratio of CO to CO₂ is 5), for the sample with the molar ratio of TiO₂: MgO:SiO₂ equal to 60:25:15, TiO₂crystal phase formed at 1873 K and 1673 K, MgTi₂O₅ formed at 1473 K. for the sample with the molar ratio of TiO₂: MgO:SiO₂ equal to 60:15:25, TiO₂crystal phase formed at 1873 K, MgTi₂O₅ formed at 1673 K and 1473 K. When the oxygen partial pressure is relatively low (volume ratio of H₂ to CO₂ is 600, 300 and 150), the precipitated crystal phase of all the samples at three different temperature were anosovite, and the content of magnesium in anosovite decreased with the reduction of oxygen partial pressure.