In order to study the mechanical properties of soil-rock mixtures dominated by the soil under a low rock content, the modeling method combining multi-layer method under compaction and random polygon generating method is adopted to establish the particle flow model of soil-rock mixture, and the inhomogeneous coefficient S is proposed as an index of the heterogeneity of soil-rock mixture. The mesoscopic parameters of the particle model were checked by a laboratory test, and the numerical simulation of the biaxial test was also carried out, for checking the effects of three factors on the mechanical properties of the soil-rock mixtures under the condition of low stone content, including the rock content, the porosity and the inhomogeneous coefficient S. In the case of low stone content, the strength of the soil-rock mixture is greatly influenced by the porosity of the soil. With the decrease of the soil porosity, the strength of the soil-rock mixtures is greatly improved. The existence of block stone destroys the uniformity and continuity of the soil. On the contrary, the overall strength of the soil-rock mixture decreases with the increase of the rock content. The inhomogeneous coefficient S has great influence on bulk strain. The greater the coefficient of heterogeneity is, the more obvious the expansion of volumetric strain is.