Abstract: Separation of acetic acid-water-butyl acetate system is a gas-liquid-liquid three phase azeotropic distillation process, and phase splitting judgment and algorithm improvement are the main issues in distillation simulation. According to published experimental data,rigorous thermodynamic models were presented to predict the activity and fugacity coefficients, and based on Gibbs free energy curves thermodynamic stability was analyzed to obtain a phase splitting criterion and phase splitting region for the acetic acid-water-butyl acetate system. Further, a new algorithm suitable for highly nonideal and multiphase distillation was developed to simulate acetic acid-water-butyl acetate distillation process. The simulation results were verified by comparison with industrial data, and the method was proved to be accurate enough to simulate the existing industrial process.