Abstract: Based on the analytical solutions for wave-induced soil response in an unsaturated hydraulically anisotropic seabed of finite thickness, a nonstandard elliptical, i.e., non-circular, rotation stress path is proven to be a more common state in a soil element due to the linear regular wave loads. Three characteristic parameters that determine the size and shape of the nonstandard elliptical rotation path are deduced. Using twenty-seven groups of undrained cyclic principal stress rotation tests, the effects of the amplitude and the initial phase difference of the normal stress difference and shear stress on the cyclic strength of saturated sand are studied. The experimental results show that the normal stress difference plays a more important role in the cyclic strength than the shear stress, and the influences of the initial phase difference on the cyclic strength are significant. The logarithmic failure cycles show an approximately linear decrease with the increasing initial phase difference, and therefore the relation of dynamic strength under two kinds of elliptical rotation stress paths, i.e., nonstandard and standard, is derived. This experimental research overcomes the drawback that the shear characteristics of sand for the traditional circular rotation stress path cannot be directly used to analyze the stability of a finite seabed, and the conclusion may provide a technical support for the design of coastal and offshore engineering.