Some results on modelling the statics of the distillation process and its applications are presented. A theoretical tray-to-lray binary distillation model is developed for describing the steady-state behaviour of composition in response to changes in bottom and reflux flows. Based on this model, a simplified one is elaborated and identified by means of the multivariable linear regression method. This approach makes it possible to find a simple and accurate model for the on-line computer control of distillation plant.