Abstract: The mechanical properties of materials discharged by stripping and stacking in open-pit mines are the key scientific problem in dump slope design and stability control. In engineering practice, the empirical method and the engineering geological analogy method are often used to estimate the mechanical parameters, but the effect of abandoned material properties and stress state on the mechanical properties is not fully considered, and the reliability of the stability calculation results of the dump slope is low. In this study, the abandoned materials of an open-pit mine in southwest China is taken as the research object, the experimental samples with different material compositions, gradation and relative densities were made by the similar gradation simulation experiment. The particle crushing mechanism and mechanical properties of each sample under different stress conditions were examined by the post shear screening experiment and large-scale triaxial shear experiment. The experimental results show that the particle breakage rate is closely related to the material compositions, gradation, relative densities and confining pressure conditions, and is strongly related to the shear strength parameters. Under the condition of low confining pressure and low relative density, the stress-strain curve has no obvious peak strength and is of the characteristic of strain hardening. The fitting curves of experimental data show that ε1/(σ1-σ3) and ε1 has a linear relation, -ε3 and ε1 has a parabola relation. Based on that fitting curve, the tangent line Poisson’s ratio μt of the abandon material is obtained, and the Duncan-Chang model is modified. The experimental test data of the contrast sample (QG-B-3) under the same experimental conditions prove that the Duncan-Chang model (modified) can describe the stress-strain characteristics of the abandon material. The shear crushing mechanism and stress-strain characteristics of the abandon materials are of important theoretical significance for dump slope deformation control in the open pit mines.