Capacity expansion and height growth of waste dump, leaded by rise of land price, have brought about geological hazards. Gradation, as the most important physical property of dump material, determines the mechanical strength of dump material and yet can hardly be investigated clearly. Therefore, revealing the disciplines of gradation is of great importance. A device for waste dump model test has been developed. Four groups of material with grain size of 0.0075 cm, 0.02 cm, 0.1-0.2 cm and 0.8-1.0 cm respectively was used to simulate the natural separation in dumping process. Then, the gradation of the dump material was analyzed by partitions. The results demonstrated that dynamic differentiation existed in the dumping process. In the vertical direction, the content of group 1 to group 3 decreased with height reduction, while the content of group 4 increased; in the horizontal direction, the content of group 1 and 2 decreased from the exterior to the inner slope, whereas the content of group 4 was on the contrary, and the content of group 3 was irregular. Besides, The FOS (factor of safety) of dump material based on the zonal model was obviously smaller than that on layered model. The results can provide a guidance for the determination of in-situ partition height to get an accurate gradation distribution with the least sampling points. In addition, the zonal model is more suitable to represent the property of the waste dump. 