<p>Rock mass excavation is accompanied by stress redistribution and disturbance-induced damage, and the mechanical response of surrounding rock is coupled and controlled by two types of effects: damage evolution and strain hardening–softening. However, existing studies still struggle to accurately characterize both in a unified theoretical framework. Therefore, this paper proposes a unified damage evolution and strain hardening–softening (UDHS) model along with the corresponding numerical implementation process. First, based on statistical damage theory, the Weibull distribution is used to characterize the statistical discreteness of rock mass strength degradation under excavation disturbance, the cumulative effect of microscopic unit failure is equivalent to the damage factor (<i>D</i>) in the generalized Hoek–Brown (GHB) criterion at the engineering scale, and an evaluation method for <i>D</i> is established. Subsequently, an equivalent Geological Strength Index (GSI_eq) is introduced, and its evolution equation is derived to respectively characterize the structural densification enhancement during the hardening stage and the relaxation degradation process during the softening stage, thereby achieving a unified description of disturbance-induced damage and structural evolution. Finally, the mechanical response law of surrounding rock under the coupling mechanism is systematically revealed. Overall, this study can provide a theoretical basis and calculation approach for the mechanical response analysis and stability assessment of surrounding rock.</p>