The solid-liquid equilibrium of succinic acid in various mass fractions of the glutaric acid + adipic acid + ethyl acetate mixture and adipic acid in various mass fractions of the succinic acid + glutaric acid + ethyl acetate mixture was measured by the dynamic method within the temperature range of 299.12 to 343.56 K under atmospheric pressure. The results show that the solubility of succinic acid and adipic acid increases with the increasing temperature. The solubility of succinic acid in ethyl acetate increases with the increase of mass fraction of glutaric acid and adipic acid in the mixed solvent at the same temperature. Similarly, the solubility of adipic acid in ethyl acetate also increases with the increase of mass fraction of succinic acid and glutaric acid in the mixed solvent. The experimental data of solubility were correlated by the Apelblat equation, the Wilson equation, and nonrandom two-liquid equation. All equations can be well applied, and the Apelblat equation has the better fitting effect. In addition, the thermodynamic properties of the mixing processes in the ternary and quaternary mixed system were calculated based on the nonrandom two-liquid model, including the mixing enthalpy, the mixing entropy, and the mixing Gibbs free energy.