Soil-rock mixture (S/RM) is a very complex discontinuous medium material, which is a multiphase system consisting of high strength rock blocks (Rocks), relatively soft filling components (Soils) and corresponding pores. Because the mechanical properties of various components of soil-rock mixtures under external loads are very different, and there are extremely complex interactions between them. Therefore, the mechanical properties of this geotechnical material (such as stress transfer, failure mode, crack propagation, bearing capacity, etc.) are quite different from those of homogeneous geotechnical materials, and largely depend on the internal structure characteristics of soil-rock mixtures (such as particle size composition, particle shape, particle distribution and arrangement). Due to the complexity of the model, the simulation of its meso-mechanical properties is mostly confined to the random simulation of regular blocks. In this paper, an automatic generation method of PFC∼2D numerical model of soil-rock mixture microstructure based on digital image processing is proposed, and the experimental simulation is carried out with matlab. Thus, the rapid, real and automatic modeling of heterogeneous material microstructure by PFC∼2D software is realized. The PFC∼2D numerical calculation model of soil-rock mixtures is established. The results show that when the stone content is 80%, the analysis should be caused by the large amount of rock, which leads to the large internal voids, and the sudden unloading between the rock and the rock during compaction and then the structural reorganization.