The current work aims to develop an extended Greenwood-Williamson (GW) model for spherical particles with surface roughness which can be incorporated into the discrete element modelling (DEM) framework.The defects of incorporating the classic GW model into DEM are fully addressed and illustrated by both theoretical and numerical results.The extended GW model which can consider the positive overlap between the sphere and nominal flat rough surface overcomes some theoretical defects of the classic GW model.The capability of this extended model is demonstrated by comparing the numerical results with that of the classic GW model and Hertz solution under the same overlap.By further introducing an elasto-plastic model,namely the CEB model,the extended model is able to account for the plastic deformation of the asperities.Empirical interaction laws are obtained based on the numerical results through a curve-fitting procedure.A simple example is presented to illustrate the effect of surface roughness on the packing behavior.