Influences of density and confining pressure on mechanical properties for coarse-grained soils were researched by four groups large-scale triaxial compression tests. The results show as follows: Density and confining pressure are important factors affect mechanical properties for one coarse-grained soil, and they decide the stress-strain curve shape. Loose coarse-grained soils usually behave strain hardening and volume shrinking, the hardening characteristic of stress-strain curve becomes distinct and the volume shrinking strain increases with the increase of confining pressure. Dense soils commonly represent strain softening and bigger volume dilatancy strain under low confining pressure, but at high confining pressure coarse-grained soils usually show hardening and volume shrinking characteristics. When the density is same, the higher the confining pressure, the higher the shear strength. If the confining pressure is equal, the residuary shear strength is equal too. The deformation is small when the initial void ratio is low under the same stress status. Density is the essential factor to decide the initial elastic modulus, and the elastic modulus in shear process is the result of combined action of stress status and density. The volumetric strain induced by shear stress is shrinking at first, then dilating later under triaxial compression test conditions, of which the value is determined by density and stress state.