Systematic　research　of　experiments　were　conducted　on　three　different　plasticity　index　clay　in　different　consolidated　condition　by　a　ring　shear　apparatus.　The　variation　of　shear　strength　in　large　deformation　and　the　effect　factors　of　residual　strength　have　also　been　investigated　by　tests.　Test　results　indicate　that　the　ring　shear　apparatus　used　in　this　study　has　good　stability　and　high　precision　for　both　silty　clay　and　clay,　thus　can　guarantee　the　accuraty　of　the　test　results;　stress　history　has　no　significant　impact　on　shear　strength　to　silty　clay　of　low　plasticity　index;　residual　strength　of　high　plasticity　index　can＇t　be　influenced　by　stress　history,　while　peak　strength　increases　with　the　increase　of　over-consolidation　ratio,　and　finally　close　to　the　peak　strength　of　silty　clay;　plasticity　index　is　an　important　factor　affecting　the　residual　strength　and　residual　strength　is　significantly　reduced　with　the　increase　of　the　plasticity　index;　the　type　of　shear　settlement　curve　related　to　the　plasticity　index　and　over-consolidation　ratio.