An efficient design method is proposed for determining the optimal design structure of a dividing wall column (DWC). The internal section of the DWC is divided into four separate sections and matched to the sloppy arrangement with three conventional simple columns. The light and heavy key component mole-fractions are used as the design variables in each column. The structure that gives superior energy efficiency in the shortcut sloppy case also brings superior energy efficiency in the DWC, while the optimal internal flow distribution of the DWC is different from that obtained from the sloppy configuration. Based upon an extensive simulation study, a two-step approach is proposed for the DWC design: the optimal DWC structure is first determined by applying the shortcut method to the sloppy configuration; the optimal internal flow distribution is then found from the corresponding DWC configuration. The simulation study shows that the DWC designed by the proposed method gives a near-optimal structure.