The thermodynamic model of a silico-ferrites of calcium and aluminum solution, SFCA phase () was newly developed in the framework of the Compound Energy Formalism (CEF). Preferred substitution of Al atoms to tetrahedral sites in the SFCA solution was verified by X-ray absorption near edge structure (XANES) analysis. On considering crystallographic information in particular the short-range-ordering nature in the SFCA solution, the  structure was considered for modeling the SFCA solution. The optimized Gibbs energies of all end-members can successfully reproduce the experimental single phase region of the SFCA solution.