A new computer simulation method is presented in this paper for random packing of particles with variable sizes in the 3-D space. This method consists of two steps of simulation: kinematics and dynamics simulations. The kinematics simulation uses a 3-D cellular registration system for efficient particle deposition. The dynamics simulation models further packing of the matrix of particles using the Discrete Element Method (DEM). The numerical model can include a large numbers of particles in the matrix for packing. A number of important details omitted in previously proposed models now can be included to increase the fidelity, allowing one to consider random sizes and the 3-D locations of particles. Application examples show that this approach is effective, compared with physical experiment results. Its application to aggregate grading for Portland cement concrete is also presented here. (C) 2003 Elsevier Science B.V. All rights reserved.