A method based on an improved genetic algorithm for the computer-aided molecular design for extractive distillation is presented. Many enhancements, including new encoding schemes and improved genetic algorithm operators, such as cross-generatent elitist selection, dislocation crossover, and mutation operators have been included. The accuracy and reliability of the method have been verified by designing the extractants for the extractive distillation processes of acetone-methanol and water-acetic acid systems. For the acetone-methanol system, the prediction precision of the relative volatility is higher in this work. For the water-acetic acid system, the average relative deviations between the predicted value and the experimental value of the infinite dilution activity coefficients of water and acetic acid in N-methylpyrrolidone (NMP) and N-methylacetamide (NMA) are 7.85% and 12.66%, respectively.