Abstract: In order to fully describe the stress-strain relations of sands along different directions in three-dimensional space, the effects of anisotropy and intermediate principal stress should be considered together. Based on the UH (unified hardening) model for sands, a three-dimensional anisotropic UH model is developed by introducing the anisotropic transformed stress method. In this method, magnitudes of the stress components along different directions are modified differently, so that the anisotropic sand can be equivalent to an isotropic sand, and the failure or yield curve in the deviatoric plane of the transformed stress space becomes a circle. If the stress tensor is replaced by the anisotropic transformed stress tensor, the UH model can be extended conveniently to consider the effects of anisotropy and intermediate principal stress. The comparisons with test results indicate that the three-dimensional anisotropic UH model can reasonably predict the stress-strain relations of anisotropic sands under a true triaxial stress state.