Abstract: To investigate the effect of the cyclic principal stress direction angle on the dynamic liquefaction characteristics of saturated coral sand, a series of undrained cyclic shear tests with 90-degree abrupt rotation of the principal stress direction are carried out using a hollow cylinder torsion shear apparatus. The test results indicate the following: The deformation behavior of the samples at liquefaction failure exhibits cyclic mobility. The contribution of each strain component to the generalized shear strain is not equal under different cyclic principal stress directions, with axial strain being predominant. Taking the principal stress direction angle α = 45° as the boundary, when α < 45°, the liquefaction resistance of coral sand samples is inversely proportional to α. When α > 45°, the greater the α, the less likely the sample is to liquefy. The normalized relationship between the generalized shear strain amplitude and the excess pore water pressure ratio is independent of the principle direction angle, relative density and cyclic stress ratio exhibiting uniqueness.