Abstract: In the Discontinuous Deformation Analysis (DDA) method a numerical model is used for analyzing the motional law in discontinuous,jointed rock masses. This method has not found wide use in engineering practice because it is relatively new and there are some limitations in both theory and application. A modified "open close" criterion and the separation of shear and normal stiffness for DDA method are proposed in this paper which make the DDA method more powerful. In modelling the excavation of a tunnel, satisfactory results have been obtained by using this new method.