Abstract: Undrained cyclic traxial tests are carried out on the saturated coral sand in Nansha Islands, South China Sea. The experiment aims at investigating the characteristics of pore water pressure,axial strain,effective stress path and cyclic resistance of coral sand under different D_r and. The differences between coral sand and Fujian sand about liquefaction characteristic are also discussed. The test results indicate that the development of pore water pressure (Δu) of coral sand is different from that of siliceous sand, which can be fitted by a modified Seed model. The accumulative energy dissipation of liquefied coral sand is greater than that of liquefied Fujian sand. The axial strain (ε_DA) of coral sand has no sudden enlargement phenomenon during cyclic loading, and the amplitude of ε_DA increases continuingly with the loading time. When touching the phase transformation line, the coral sand shows the alternation of dilatancy and contraction as the effective stress still exists. Compared with the Fujian sand, the coral sand has a greater fluctuation in especially when approaching, and a phenomenon of transient liquefaction can be observed in the tests. The cyclic resistance of coral sand increases with the increase of D_r and. The cyclic resistance of coral sand is basically higher than that of siliceous sand.