It　is　imperative　to　study　the　engineering　characteristics　of　residual　soils　which　is　weathered　violently　under　large　deformation.　Making　use　of　the　test　features　of　ring　shear　apparatus,　the　change　law　of　shear　strength　of　soils　under　large　shear　displacement　can　be　studied.　The　experimental　determination　of　residual　strength　and　peak　strength　indexes　of　residual　soil　is　conducted　by　ring　shear　tests.　Test　data　are　analyzed　through　arrangement　and　comparison.　The　relationship　between　water　content　and　residual　strength　proved　the　existence　of　property　of　watering　softening　under　large　deformation.　The　character　of　strain　softening　of　residual　soil　is　analyzed　by　strain　threshold,　that　is,　various　shear　strengths　should　be　different　with　various　shear　displacements.　Specifically,　the　peak　strength　corresponding　to　the　range　of　strain　is　between　0.02　and　0.06　while　the　residual　strength　corresponding　to　the　range　of　strain　is　between　0.06　and　0.20.　Besides,　the　results　also　indicate　that　the　residual　strength　of　residual　soil　is　directly　affected　by　the　difference　of　mineral　composition,　which　is　the　internal　cause　of　inhomogeneity　of　residual　soils.