Abstract: Using the ring shear apparatus, the variation rules of residual strength of 17 saturated claysoil samples with different plasticity indices under different consolidation conditions are studied. The influences of current normal stress, over-consolidation ratio, plastic index and multistage shear mode on the residual strength are analyzed. The variation of shear strength index with different plasticity indices under large deformation and the corresponding practical formula are investigated. The test results show that with the increase of the current normal stress, the residual strength increases. The over-consolidation ratio does not have a significant impact on the residual strength. With the increase of the plasticity index, the residual strength reduces gradually. Under the small stress level the residual strength is nonlinear. Under large deformation, the residual internal friction angle increases while the plasticity index decreases. Finally, the formula for the relation between the residual internal friction angle and the plasticity index is proposed.