Abstract: The deep surrounding rock in the process of excavation exhibits complex post-peak mechanical properties. It has long been an issue of great concern to the engineering. Thorough studies on the post-peak mechanical properties are of great significance to resource extraction projects. Based on the deep shaft horsehead project, the mechanical post-peak properties of the granite are studied by using laboratory tests. The nonlinear fitting method is used to obtain the exponential relationship between the post-peak softening modulus and confining pressure of granite. The rock dilatancy angle is assumed to be constant. A post-peak strain softening model is established considering confining pressure and dilatancy angle based on the theory of plasticity. Using FLAC^3D as the platform to develop and validate a mathematical model for horsehead tunnel to analyze the failure rules of the deep surrounding rock under strain softening conditions. The research results show that the post-peak destruction of granite has a trend of brittle to ductile transformation. Under high confining pressure, it exhibits plastic softening damage characteristic. The post-peak softening modulus increases with the decrease of the confining pressure. The FLAC^3D numerical verification shows that the results of the strain softening model agree with the experimental data, and that the proposed model is reliable. By analyzing the properties of horsehead roadway damage through numerical simulation, it is found that the plastic shear strain appeares in partial areas, such as the vault and arch foot, and that the location and depth are similar to the field ones.