A　multiscale　method　is　presented　to　develop　a　constitutive　model　for　anisotropic　soils　in　a　three-dimensional　(3D)　stress　state.　A　fabric　tensor　and　its　evolution,　which　quantify　the　particle　arrangement　at　the　microscale,　are　adopted　to　describe　the　effects　of　the　inherent　and　induced　anisotropy　on　the　mechanical　behaviors　at　the　macroscale.　Using　two　steps　of　stress　mapping,　the　deformation　and　failure　of　anisotropic　soil　under　the　3D　stress　state　are　equivalent　to　those　of　isotropic　soil　under　the　triaxial　compression　stress　state.　A　series　of　discrete　element　method　(DEM)　simulations　are　conducted　to　preliminarily　verify　this　equivalence.　Based　on　the　above　method,　the　obtained　anisotropic　yield　surface　is　continuous　and　smooth.　Then,　a　fabric　evolution　law　is　established　according　to　the　DEM　simulation　results.　Compared　with　the　rotational　hardening　law,　the　fabric　evolution　law　can　also　make　the　yield　surface　rotate　during　the　loading　process,　and　it　can　grasp　the　microscopic　mechanism　of　soil　deformation.　As　an　example,　an　anisotropic　modified　Cam-clay　model　is　developed,　and　its　performance　validates　the　ability　of　the　proposed　method　to　account　for　the　effect　of　soil　anisotropy.　©　2024　by　the　authors.