A new strategy for the optimal design of a distillation column is developed. Major difficulties in the op-timal design of a distillation column are such facts that the number of stages is discrete and the total number of model-ing equations varies with the number of stages. In this study, Two-Tier Approach in which both rigorous and reduced model exist is applied to solve such difficulties. Reduced model is composed of equations only and the numbers of stages in the column sections are treated as real variables. In these respects, optimization calculation is performed with reduced model and rigorous simulation follows on the basis of the results obtained. The recursive execution of the above mentioned optimization and simulation step results in the optimal design of distillation column. ODDS(Optimal Design of Distillation System)system which implemented Two-Trier Approach is developed. ODDS system is proved to be effective by case studies though not perfect yet.