<p>Soil-rock mixture (S-RM), as an easily accessible backfill material, has been widely used in engineering construction in southwestern China, northern India, western USA and other regions. The mechanical properties of S-RM are very complex, and their structural effects directly affect the stability and safety of engineering construction. Therefore, it is necessary to conduct a systematic study on the structural effects of S-RM. Triaxial tests based on the discrete element method (DEM) are an effective way to simulate the structural effects of S-RM, but the fineness of the modeling method determines the accuracy of the simulation results. Firstly, this study developed a rock blocks modeling method based on DEM considering the real shape. Secondly, a flexible loading boundary of the triaxial test was fully considered, and a discrete element numerical model of the S-RM under the triaxial test conditions was established. And the method was validated using laboratory tests. Finally, the structural effects of rock block content (RBC) were analyzed. The results showed that the rock block rotation, contact force chain distribution, microcracks distribution, deviatoric stress–strain curve, volumetric strain, shear failure plane, and shear strength parameters within the specimen changed regularly as the RBC increased. Generally, the RBC of the specimen has a significant structural effect on both the strength and deformation of S-RM.</p>