Packing model of aggregate is a very important issue in gradation design and research on asphalt mixture. The packing characteristics of coarse aggregate and fine aggregate can affect the skeleton and volumetric parameters, such as VMA (Void in Mineral Aggregate), of asphalt mixture respectively. In this study, based on the ideal packing model of aggregate, the 2?D packing model which is a random distribution and compacted contact of different size aggregates is built, and the mathematic solution to this model is figured out by using the geometric theory of space topology. The model has been programmed and visualized by using Visual Basic language. The impact of gradation on the skeleton and VCA (Void in Coarse Aggregate), and the effect of fine aggregate packing on VMA can be analyzed by using this model and algorithm. The model is helpful to the gradation design, analysis and evaluation for asphalt mixture.