Abstract The thermodynamic evaluation and optimizations of the KF-CrF 3 and NaF-CrF 3 systems were carried out within the framework of CALPHAD (CALculation of PHAse of Diagrams) approach. The liquid phase was described by the associated solution model, and the intermediate phase were treated as stoichiometric compound model. All the model parameters were optimized based on the experimental phase equilibria data from experimental measurements and theoretical predictions (First-principles calculation and empirical equation). A set of self-consistent and reliable thermodynamic parameters was obtained, which can well describe the phase equilibria and thermodynamic properties of the KF-CrF 3 and NaF-CrF 3 system. Furthermore, the database for the LiF-NaF-KF-CrF 3 quaternary system was preliminarily established using Muggianu extrapolation model. Meanwhile, the solubility of CrF 3 in FLiNaK at different temperatures was obtained. The calculated value is in good agreement with the reported measurements by ORNL, considering kinetic factor of K 3 CrF 6 involved in FLiNaK.