The　failure　of　material　can　be　concluded　to　the　shear　fracture　and　each　material　has　a　specific　shear　sliding　surface.　The　shear　strength　is　the　function　of　normal　stress　on　sliding　surface.　A　series　of　shear　sliding　surface　is　unified　and　nonlinear　unified　strength　model　of　geo-materials　is　proposed.　Sliding　surface　of　nonlinear　unified　strength　model　is　isoclinic　surface　in　β　stress　space.　The　Strength　surface　of　nonlinear　unified　strength　model　is　circular　conical　surface　in　the　β　stress　space　and　a　series　of　conical　surfaces　are　continuous　smooth　and　convex　in　principal　stress　space.　The　nonlinear　unified　strength　model　can　be　illustrated　as　a　curve　between　the　Drucker-Prager　and　SMP　in　deviatoric　plane,　and　as　a　straight　line　in　meridian　plane.　There　are　only　three　mechanical　parameters　in　the　model　which　have　definite　physical　meanings.　Compared　with　large　numbers　of　data　under　true　triaxial　tests,　the　applicability　of　nonlinear　unified　strength　model　is　verified　to　different　materials.　And　the　proposed　model　can　describe　the　nonlinear　strength　property　of　various　materials　reasonably.