The strength and deformation characteristics of coarse-grained soil are closely related to the initial gradation and dry density during specimen preparation. To study the strength and deformation characteristics of coarse-grain materials with different gradations and densities, a simple and generalized method for calculating the skeleton void ratio of coarse-grained soil is proposed. The results of laboratory tests show that there is an obvious monotonic variation between the skeleton void ratio obtained by this calculation method and the mechanical properties of coarse-grained soil. When the specimen size is consistent, with the decrease of the skeleton void ratio, the failure shear stress increases, the failure friction angle increases, and the cohesion decreases. Also, as the skeleton void ratio decreases, the average initial tangent elastic modulus increases and the average initial tangent Poisson's ratio decreases. On the whole, the smaller the skeleton void ratio, the greater the strength and stiffness of the coarse-grained soil. Based on this, a scale-down method of coarse-grained soil with equivalent skeleton void ratio is proposed in this paper.