Abstract: The contact interface between the soil-rock mixture and the bedrock is often a potential slip surface that cannot be ignored for the instability of highly-filled slopes and natural slopes. Through the large-scale direct shear tests in the laboratory and the numerical simulations using the discrete element software, the influences of stone content on the shear mechanical properties of the soil-rock mixture-bedrock interface and the shear failure mechanism of the contact surface are investigated. The results show that the shear stress-shear displacement curve of the soil-rock mixture-bedrock interface changes from strain softening to strain hardening with the increase of normal pressure. The "V-shaped jump" in the shear stress-shear displacement curve is mainly related to particle breakage, rotation and overturning. The shear strength and shear strength indexes of the soil-rock mixture-bedrock interface increase first and then decrease with the increase of rock content, and there is an optimal stone content to maximize the shear strength, but the internal friction angle φ does not change significantly and fluctuates around 38°. The distribution and morphology of the shear zone are significantly affected by the stone content and normal pressure. The higher the normal pressure and rock content, the thicker the shear zone. The failure of the block stones in the shear band can be divided into three modes: surface grinding, partial crushing and complete crushing. The normal pressure and stone content are the reasons that affect the relative crushing rate B_r. The specific performance is that with the increase of the stone content and normal pressure, the relative crushing rate of block stones increases continuously.