The　strength　and　deformation　characteristics　of　rocks　are　the　most　important　mechanical　properties　for　rock　engineering　constructions.　A　new　nonlinear　strength　criterion　is　developed　for　rocks　by　combining　the　Hoek-Brown　(HB)　criterion　and　the　nonlinear　unified　strength　criterion　(NUSC).　The　proposed　criterion　takes　account　of　the　intermediate　principal　stress　effect　against　HB　criterion,　as　well　as　being　nonlinear　in　the　meridian　plane　against　NUSC.　Only　three　parameters　are　required　to　be　determined　by　experiments,　including　the　two　HB　parameters　sigma(c)　and　m(i)　.　The　failure　surface　of　the　proposed　criterion　is　continuous,　smooth　and　convex.　The　proposed　criterion　fits　the　true　triaxial　test　data　well　and　performs　better　than　the　other　three　existing　criteria.　Then,　by　introducing　the　Geological　Strength　Index,　the　proposed　criterion　is　extended　to　rock　masses　and　predicts　the　test　data　well.　Finally,　based　on　the　proposed　criterion,　a　triaxial　elasto-plastic　damage　model　for　intact　rock　is　developed.　The　plastic　part　is　based　on　the　effective　stress,　whose　yield　function　is　developed　by　the　proposed　criterion.　For　the　damage　part,　the　evolution　function　is　assumed　to　have　an　exponential　form.　The　performance　of　the　constitutive　model　shows　good　agreement　with　the　results　of　experimental　tests.