A numerical method is proposed for the simulation of a long adsorption column. This method computes only the movement of and the change inside the mass transfer zone. The movement of the mass transfer zone is solved implicitly by conforming to some appropriate boundary condition. The interior of the mass transfer zone is solved by the orthogonal collocation method. The simulation of a LDF model with a Langmuir isotherm is given to demonstrate the general procedure of this method. Comparison is made to the exact solutions, as well as the solutions of the conventional fixed-node collocation method. The proposed method gives an accurate prediction of the breakthrough curve with just a few collocation points. The accuracy of the prediction is independent of the column length. It is therefore most suitable for the simulation of a long adsorption column. The extension to a multicomponent system is also discussed.