The basic phase is selected according to the measured phase diagram, two isothermal sections and two vertical sections of the Al 2O 3-CaO-SiO 2 ternary system are calculated using FACT software. The sections in the same conditions are described through the measured phase diagram. Because of the complexity of this ternary system, there is a large difference between the measured and the calculated phase diagram. It is necessary for FACT to ameliorate the calculation model and perfect the database in calculating oxide system which the interaction is strong. For this kind system, the isothermal section and vertical section should be founded through the experiment result and referencing the calculated phase diagram at the same time.