A critical evaluation and thermodynamic optimization of all the available literature experimental data of the CaO-CaF₂ system was conducted to obtain a set of thermodynamic functions which can reproduce all available and reliable experimental phase diagrams and thermodynamic data. The liquid solution was described using the Modified Quasichemical Model which assumes the mixing of O² and F⁻ in the pseudo anionic sublattice and CaF₂ solid solution was described using the compound energy formalism. The discrepancies in the CaO and CaF₂ liquidii among the available experimental data were resolved. The recent experimental data on the solubility of CaO in solid CaF₂ phase were well reproduced, which is critical to explain the eutectic temperature of the system.