The　elastoplastic　constitutive　model　for　concrete　material　often　employs　the　shear　yield　surface　which　includes　two　kinds　of　hardening　modes,　namely,　cohesion　(c)　hardening　and　friction　(φ)　hardening.　Most　of　existing　constitutive　models　employed　c　hardening　mode　which　is　not　able　to　reflect　the　stress　induced　anisotropy.　The　yield　surface　in　this　paper　is　developed　by　nonlinear　unified　strength　criterion　for　concrete,　and　the　φ　hardening　mode　is　used.　A　unified　hardening/softening　parameter　is　proposed　on　the　bases　of　the　uniaxial　compressive　stress-strain　relation　proposed　by　Sargin.　Then　a　3D　unified　hardening/softening　elastoplastic　constitutive　model　is　established　by　combing　the　hardening/softening　parameter　with　the　yield　surface.　The　developed　model　is　capable　of　describing　the　hardening　and　softening　uniformly.　Therefore,　the　computational　efficiency　of　numerical　analysis　is　increased.　The　model　gives　the　determination　of　the　plastic　potential　parameter,　which　makes　the　dilatancy　can　be　controlled　reasonably.　Moreover,　the　relationship　between　the　equivalent　plastic　shear　strain　related　to　the　peak　stress　and　confining　pressure　is　supposed　by　the　test　results.　Thus　the　model　can　reasonably　describe　the　change　rules　of　strain　softening　of　concrete　with　the　confining　pressure.　Comparisons　with　the　biaxial　and　triaxial　tests　of　high　strength　and　normal　strength　concrete　indicate　that　the　proposed　model　is　suitable　for　various　kinds　of　concrete　materials,　and　can　reasonably　describe　the　3D　deformation　and　strength　properties　of　concretes.　©　2016　Chin　J　Biotech,　All　right　reserved.