Abstract: The resonant column tests on the effects of relative density and confining pressure on the maximum modulus and damping ratio of coral sand in South China Sea under small strain are performed. The test results show that, for the samples with the same relative density, the maximum shear modulus of coral sand increases with the increasing confining pressure, while the damping ratio decreases with the increasing confining pressure. For the samples under the same condition of confining pressure, the maximum shear modulus of coral sand increases with the increasing relative density, while the damping ratio decreases with the increasing relative density. Based on the test data, the variation rules of the maximum shear modulus and damping ratio of coral sands considering confining pressure and relative density are established, which can provide the basic data and technical support for infrastructure construction in the coral sand areas of South China Sea.