A unified excess Gibbs function model is proposed for mixed-electrolyte mixed-solvent systems by superposing a short-range interaction derived from a new lattice-hole-based Helmholtz free energy on the electrostatic interaction. The short-range interaction energy is represented by the sum of electrostatic and nonelectrostatic interactions, the former being expressed by a universal function of distance parameter of ions. With two parameters for solvents and three parameters for ions, the model was found to describe various properties with average root mean square errors from 2-4%. For a system with some complex oxy anions, a counterion parameter is needed. The model was found useful for various predictions including vapor-liquid equilibria.