Abstract: As a basic attribute of Soil-Rock Mixtures(S-RMs), particle breakage has complex formation mechanism and many influencing factors. To systematically explore the influencing factors and basic laws of the breakage characteristics of S-RMs, we construct a PFC^2D particle discrete element numerical model by the thought of Monte Carlo. The model can truly reflect the breakage process of the rock block. Based on the indoor direct shear test and screening test, we carry out a series of numerical shear tests. The results show that: the sample appears obvious breakage phenomenon after shearing to disperse stress. The diameter of rock block has a significant effect on the breakage degree of rock block. The larger the diameter of rock block is, the greater the breakage potential is, and the easier it is to be broken. When the edges and corners of rock block are obvious, the stress concentration degree is stronger, and the breakage rate is larger. When the grain group is continuous and good, the particles contact more and completely, so the interface is larger and the breakage is less likely to occur. The initial porosity of the sample has little effect on the breakage rate. Under the same normal stress, with the increase of porosity, the breakage degree of the rock block shows a slight increasing trend.