Abstract: A mathematical model for complex systems of interlinked distillation columns is presented. Because of the presence of interlinked streams, a small number of nonzero off-tridiagonal elements occurred in the blocks matrix and consequently complicated the procedure of solution. The method presented in this paper adopted the basic procedure developed by Browne for solving multicolumn equilibrium stages, and improved his convergence criteria. In order to make use of mass storage efficiently during the solution, the e-limination form of inverse(EFI) and product form of inverse(PFI) were used, so as to provide the possibility for solving large-scale problems. Examples cited from the literature were calculated with satisfactory results.