The Conventional triaxial consolidation drainage shear tests under different confining pressures were carried out for three kinds of non-viscous coarse particles in the overburden of a dam, and the effects of different relative compactness on mechanical properties of coarse particles were studied. The results show that before reaching the peak strength, with the increase of relative density and confining pressure, the initial tangent modulus and peak strength increase correspondingly. The relationship between the initial tangent modulus and confining pressure is a power function under the same relative density. Under the same confining pressure, with the increase of relative density, the stress-strain curve shows a more obvious softening phenomenon. The dilatancy of the sample gradually increases, and the axial strain corresponding to the peak strength gradually decreases. The relative density has a great influence on the deviator stress of the sample during failure, but has little influence on the residual deviator stress. Meanwhile, the study found that the parameters R_f and n of the Duncan-Chang model are basically not affected by the density, and K has a positive correlation with the density. A new parameter λ is introduced to quantitatively analyze the relation of parameter λ with confining pressure and compactness. The relationship between the strength index and the relative density is linear, and the relationship between the shear strength index and the relative density is given.