Abstract: Eight large-scale triaxial tests on coarse-grained soil with different lithologies are carried out. The effects of gradation on strength, deformation, dilatancy and particle breakage characteristics of coarse-grained soil are discussed. The test results show that the grain-size composition is the important factor for the mechanical properties, and the strength and deformation characteristics change with the content of fine particles and the mud content. The particle breakage and the peak value of shear stress with the change of confining pressure and gradation are discussed. For the cohesionless coarse-grained soil with the same density, the strength and the stiffness increase with the increase of the fine-grained contents under high stress. For the cohesive coarse-grained soil, the strength and the stiffness of the materials with high mud content are smaller than those with low mud content. Good gradation and strict control of particle content less than 0.075 mm are propitious to improve the stability of the dam body and reduce the dam settlement for high earth and rockfill dams.