Abstract: Based on minimization of Gibbs free energy，a genetic algorithm (GA) was developed for the calculation of phase equilibria and stability in multiphase reaction systems. The total optimization problem was decomposed into two sub-problems，i.e. the minimization of Gibbs free energy for any postulated phases was first solved and then the phase stability analysis for each postulated phases was performed based on the tangent plane distance criterion. By adding sequentially new phases into the system and solving the two sub-problems with the genetic algorithm，the final phase distribution and equilibrium compositions would be obtained. Two complex examples were solved. One was the synthesis of methanol in a high pressure system and the other was the esterification reaction. The results obtained showed that the suggested approach was effective for the addressed problem.