A series of large-scale triaxial tests are conducted on the influence of particle grading and relative density on the strength and deformation characteristics of sandy gravel with high content of particles smaller than 5 mm. It shows that the compaction performance of sandy gravel decreases with the increasing mass fraction of particle less than 5 mm. Strength parameters and deformation parameters increase with the increase of the mass fraction of particles larger than 5 mm P 5 and relative density Dr. The strength parameters, c, φ, φ 0 and Δ φ ,increase linearly with the growth of P 5 and Dr, and there is almost no interaction between influences of P 5 and Dr on strength parameters. The test results also show that the Duncan E-B model parameters K and K b increase with the growth of P 5 and Dr, the effects of Dr on K and K b are greater for sandy gravel with higher content of particles larger than 5 mm, and the effects of P 5 on K and K b are more significant for sandy gravel with higher relative density. The empirical formulas, considering the effects of particle grading and Dr, are proposed to predict mechanical properties and Duncan E-B model parameters, and the formulas have high precision in prediction of mechanical indexes of poorly-graded sandy gravel with high content of fine particles for overburden in Poyang Lake area.