As　the　critical　dynamic　parameters　for　soil,　an　extensive　examination　of　the　dynamic　elastic　modulus　Ed　and　damping　ratio　lambda　in　coarse-grained　soil　is　of　significant　theoretical　and　practical　importance.　Currently,　there　is　a　scarcity　of　experimental　equipment　and　methods　for　measuring　the　dynamic　elastic　modulus　and　damping　ratio　of　coarse-grained　soils.　Moreover,　studies　examining　the　influence　of　relative　density　on　these　parameters　in　coarse-grained　soils　are　largely　absent.　To　investigate　the　behavior　of　the　dynamic　elastic　modulus　and　damping　ratio　in　coarse-grained　soil　under　varying　relative　densities,　a　number　of　dynamic　triaxial　tests　were　conducted　on　a　specific　coarse-grained　soil　using　the　DYNTTS　type　dynamic　triaxial　test　apparatus.　The　findings　reveal　that,　under　various　gradations,　the　Ed　of　coarse-grained　soils　exhibits　a　decreasing　trend　with　increasing　dynamic　strain,　a　trend　that　intensifies　with　higher　relative　densities.　Additionally,　as　relative　density　increases,　the　degradation　rate　of　the　dynamic　shear　modulus　ratio　Gd/Gdmax　to　dynamic　shear　strain　gamma　d　curve　escalates.　The　maximum　dynamic　shear　modulus　Gdmax　rises　with　increasing　relative　density　Dr,　displaying　a　linear　relationship　between　Gdmax　and　Dr.　Furthermore,　both　the　increasing　rate　of　lambda　to　gamma　d　curve　and　the　maximum　damping　ratio　lambda　max　progressively　diminish　with　the　escalation　of　relative　density　Dr.　Notably,　the　maximum　damping　ratio　has　a　power　function　relationship　with　the　relative　density.