This　paper　proposes　a　constitutive　model　for　soil-structure　interfaces　by　combining　the　tangential　stress-strain　relation　and　normal　stress-strain　relation　of　contact　surface　soils.　Based　on　the　analysis　of　the　deformation　properties　of　the　soil-structure　interface　and　the　shear　slip　plane　of　the　soil　on　the　interface　corresponding　to　octahedral　surfaces　under　unit　body　3D　stress　states,　the　tangential　stress-strain　relation　is　established　by　applying　the　3D　elastoplastic　constitutive　model　for　soils　to　the　octahedral　surface.　The　normal　compressive　deformation　of　the　soil　on　the　interface　is　similar　to　that　of　side-limit　condition.　Therefore,　the　normal　stress-strain　relationship　of　the　soil　on　the　interface　is　established　on　the　basis　of　the　loading-deformation　relation　under　the　side-limit　condition.　The　proposed　constitutive　model　has　only　four　material　parameters　with　clear　physical　meanings.　These　four　parameters　can　be　determined　through　the　isotropic　compression　test　and　the　conventional　triaxial　compression　test.　Comparisons　between　the　proposed　constitutive　model　and　test　results　of　the　soil　on　the　interface　indicate　that　the　model　is　capable　of　reasonably　describing　the　tangential　softening　and　hardening　characteristics　and　normal　deformation　rules　of　the　soil　on　the　surface.　Furthermore,　the　proposed　model　is　integrated　in　the　general　finite　element　package　ABAQUS　via　FRIC　to　simulate　the　deformation　process　of　the　soil　on　the　interface.　The　simulations　show　that　the　FRIC　subroutine　is　able　to　reflect　the　nonlinear　mechanical　behavior　of　the　soil-structure　interface.　©　2017,　Engineering　Mechanics　Press.　All　right　reserved.