Thermodynamic properties and vaporization processes in the melts of the SrO-Al2O3-SiO2 system were studied using the Knudsen effusion mass spectrometric method in the temperature range 1800–2400 K. The partial pressures of the Sr and SiO vapor species, activities of components, as well as Gibbs energies illustrated the negative deviations from the ideality in the system under consideration. The obtained experimental values of thermodynamic properties in the SrO-Al2O3-SiO2 system were compared with the corresponding functions calculated using the semi-empirical Kohler method and obtained as the result of modeling using generalized lattice theory of associated solutions. The mutual agreement between experimental, calculated, and modeling data was convincingly shown, which allows usage of the thermodynamic data found as well as the model approaches mentioned above for the further application in the studies based on the CALPHAD method for the prediction of thermodynamic properties and phase equilibria in advanced multicomponent oxide systems and materials at high temperatures.