Abstract: The nonlinearity and inhomogeneity of rock mass are manifested at any scale. Geometric equations and constitutive equations based on the continuity assumption cannot accurately characterize the post-peak deformation and failure processes of engineering rock masses. Considering the practical shortcomings of continuum mechanics in solving the stress and deformation in surrounding rock, this study employs only boundary conditions and equilibrium equations, and describes the stress distribution in the surrounding rock softening zone via an averaging approximation. Furthermore, the initial radius of the softening zone of circular openings estimated, and the softening law of the post-peak internal friction angle is back-calculated. The results show that the softening law can be well described by the Boltzmann function. In addition, the mass conservation law is applied to analyze the deformation of the surrounding rock. The research results can provide theoretical reference for the design of long-term stability support in deep underground engineering.