A　simple　single　bounding　surface　constitutive　model　is　developed　to　predict　the　undrained　behaviours　of　saturated　clays　under　cyclic　loads.　The　new　model　does　not　involve　complex　kinematic　hardening　rules,　and　it　is　only　required　to　memorize　important　stress　reverse　events;　therefore,　the　simplicity　should　be　the　largest　advantage　of　the　model.　A　new　interpolation　function　of　an　elastoplastic　shear　modulus　is　proposed　based　on　bounding　surface　theories.　The　evolution　of　a　hardening　modulus　is　described　in　the　deviatoric　stress　space　by　the　movement　and　updating　of　a　mapping　centre　based　on　the　new　interpolation　function,　which　enables　the　model　to　describe　the　stress-strain　hysteretic　responses　of　clays　under　cyclic　loading.　The　new　model　can　be　regarded　as　an　improvement　of　some　classical　one-dimensional　soil　dynamic　models　and　a　generalization　in　three-dimensional　stress　space.　The　model　parameters　can　usually　be　determined　by　performing　triaxial　tests.　The　model　performance　has　been　verified　by　a　comparative　analysis　on　clays　subjected　to　one-way　and　two-way　cyclic　loading　at　different　stress　levels.　The　developed　model　can　capture　the　essential　features　of　behaviours　in　saturated　clay,　including　reverse　plastic　flow,　evolution　of　hysteretic　loops,　accumulation　of　plastic　deformations　and　soil　stiffness　degradation.　The　newly　developed　constitutive　model　has　been　successfully　encoded　into　the　ABAQUS　software　package　by　the　secondary　development　interface　of　UMAT.　The　ability　of　the　model　to　calculate　boundary　value　problems,　such　as　clay　foundations　subjected　to　seismic　loads,　has　been　verified　to　some　extent　by　simulating　the　seismic　responses　of　homogeneous　horizontal　sites.