Abstract: Soil-rock mixture is a natural geomaterial with multiple grain grades and has dramatic trans-scale and hierarchical natural characteristics. Soil-rock mixture was decomposed into the matrix and rock blocks according to the mesoscale kinematic characteristics to investigate the influence of rock blocks on its shear strength. Based on the shear stress flow-around effect and Eshelby-Mori-Tanaka method, a mechanism-based shear strength theoretical model was proposed. Moreover, three groups of soil-rock mixture samples with different rock block contents were prepared for a large-scale direct shear tests to study the rock block effect of the soil-rock mixture. Meanwhile, mesoscopic parameters of the proposed model were quantitatively studied. The experimental and theoretical results show that the rock blocks significantly affect the deformation characteristics of the soil-rock mixture and its shear strength increases with the increase in the rock block content. The action of the shear stress flow-around effect that causes the rock blocks to generate rotation resistance and the matrix around the rock block to appear stress concentration, which leads to more energy storage from the soil-rock mixture compared with that of the pure matrix under the same deformation, is the mesoscopic physical mechanism of the enhanced shear strength caused by the rock blocks. The shear strength of soil-rock mixture predicted by the mesoscopic model is in good agreement with that of the test result.