Phase equilibrium relations for the CaO–SiO2–TiO2-10 wt%Al2O3 system were studied at 1300 °C and 1400 °C by a high temperature equilibration and quenching method, with the purpose of extending the equilibrium phase information for the TiO2-containing slag systems. Equilibrium phase assemblies and phase compositions were analyzed by Scanning Electron Microscopy (SEM) equipped with an X-ray Energy Dispersive Spectroscopy (EDS). The equilibrium solid phases of perovskite CaO·TiO2, wollastonite CaO·SiO2, rutile TiO2, silica SiO2 and sphene CaO·SiO2·TiO2 were confirmed to coexist with a liquid phase. Based on the experimental results, the 1300 °C and 1400 °C isotherms were constructed in the CaO–SiO2–TiO2-10 wt% Al2O3 quasi-ternary phase diagram. Significant discrepancies were found between the present results and the simulated results by FactSage and MTDATA databases, as well as the results from previous literature.