To investigate the impact of rock block proportion (RBP) on shear properties and meso-failure mechanism of mudstone soil-rock mixture (SRM). Four groups of sample with RBP ranging from 0% to 80% were prepared for large-scale triaxial tests under three different confining pressures (0.2、0.4、0.6、0.8 MPa). and the change rules of deviatoric stress、volumetric strain and shear strength of sample with different RBPS. Then, a series of numerical analysis were conducted based on particle flow numerical method PFC2D by digital image processing. It is shown that the shear strength increases with the increase of RBP. Unlike other types of soil-rock mixture, sample shows the law of shearing contraction and then dilatation under low confining pressure, and the stronger the final shear dilatation with the higher RBP. The shear contraction decreases under high confining pressure, and the stronger the final shear contraction with lower RBP. With the increase of SRM, the internal friction angle shows slow-fast-slow and "S" growth trend and growth faster between 20%~80% RBP. The cohesion decreases all the time, but the rate of decline is decreasing. Numerical tests indicate that the failure of SRM is tension-shear mixing failure during shear tests. The skeleton-effect of rock blocks becomes more and more obvious with the increase of SRM, the shear zone bypassing the rock blocks and multiple irregular and small shear zone is formed.