Genetic algorithm for the calculation of combustion equilibrium composition was proposed based on the principles of chemical equilibrium and the method of minimum free energy. By determining the independent variables and its range, the fitness function was confirmed. To validate the accuracy of the genetic algorithm, the calculation results were compared with the data from references experiment. Results show that the calculation values agree well with the reference data with error less than 1% and 1.5% for combustion equilibrium composition and combustion temperature of negative-oxygen compounds, and less than 7.7% and 5% for that of oxygen-enriched compounds. And the theoretic calculations are well coincident with those obtained by tests of hydroxyl-terminated polybutadiene solid Propellants. The maximum error between them is 4.27%, which demonstrates that the genetic algorithm can be used in compound design, performance prediction and combustion products confirming.