The hybrid method was adopted to model the original gradation of a rock-fill material according to the code, and three simulated gradations of rock-fill material have been obtained. By the same token, their equivalent particle diameters are 20 mm, 40 mm, and 60 mm, respectively. With samples prepared under the criterion of a same relative density, the scale effect on strength and deformation characteristics of the rock-fill material were studied by large/medium-scale and consolidated-drained triaxial compression tests. The results show that the nonlinear strength indexes, φ₀ and Δφ, have an increasing trend of a logarithm function with the maximum grain diameter d_max of rock-fill material. Through analyzing the influences of particle size and confining pressure on the axial strains and volumetric strains, some useful conclusion can be drawn as: both the initial elastic modulus E_i and the tangent volumetric modulus B_t increase with the maximum grain size d_max, and there is a good linear relationships between the initial elastic modulus and the maximum grain size as well as that between the tangent volume modulus and the maximum grain size; the initial Poisson’s ratio ν_i decreases with the maximum grain size d_max, and there is a good exponential relationship between the initial Poisson’s ratio and the maximum grain size. Meanwhile, formulas considering the initial elastic modulus, the initial Poisson’s ratio, the tangent volume modulus, the maximum grain size and the confining pressure were obtained, which can roughly estimate the effect of maximum grain size on the initial elastic modulus, the tangent volumetric modulus and the initial Poisson’s ratio.