In　order　to　describe　the　thermomechanical　deformation　and　shape　memory　effect　of　shape　memory　polymers　(SMPs),　a　three-dimensional　thermomechanical　constitutive　model　that　considers　elastic,　viscoelastic　strain　and　thermal　expansion　is　proposed　for　isotropic　SMPs.　A　three-dimensional　finite　element　procedure　is　developed　by　implementing　the　proposed　constitutive　model　into　the　user　material　subroutine　(UMAT)　in　ABAQUS　program.　Numerical　examples　are　used　to　compare　it　with　existing　experimental　data　in　a　one　dimensional　case　and　to　demonstrate　the　thermomechanical　behavior　of　SMPs　with　3D　deformation.　It　is　shown　that　the　present　constitutive　theory　and　the　finite　element　method　can　effectively　simulate　the　thermomechanical　behavior　and　shape　memory　effect　of　SMPs　under　complicated　deformation　states.