Abstract: To explore the influence of sedimentation direction (φ_d) on the undrained cyclic response of Nansha coral sand, a series of undrained cyclic shear tests under complex loading conditions were conducted. The test results showed that φ_d had a significant impact on the development trend of excess pore water pressure (u_e) and generalized shear strain (γ_g) of saturated coral sand, and that the development mode of u_e was diverse. The coupling effect of cyclic stress path and the sedimentation angle significantly affects the cyclic shear resistance of saturated coral sand. As the direction of initial cyclic principal stress (α_d) increases, the difference in liquefaction resistance of saturated coral sand under different φ_d decreases. When α_d = 45°, the difference in liquefaction resistance is minimized. Based on the analysis of the relationship between the sedimentation angle and the shear band angle, a coefficient λ suitable for describing the influence of φ_d on the cyclic shear strength of coral sand is proposed to correct the unit cyclic stress ratio (USR). When using the modified unit cyclic stress ratio (USR_φ) considering φ_d as the stress level index, the discreteness of experimental data points is significantly reduced, and a good unique relationship can be found between USR_φ and N_f.