<p>To study the evolution law of the mechanical properties of a fractured rock mass under confining pressure, the strength degradation mechanism of a rock mass with different fracture penetration degrees is explored from a macro–micro perspective based on triaxial compression tests, and then the nonlinear influence of structural defects on the rock mass damage and failure are characterized. The results show that, as the confining pressure increases, microcracks and pores inside the rock gradually develop and fracture defects are rapidly activated. The stress concentration at the fracture tip is obvious, resulting in different fracture rock failure modes (0%, 25%, 50%, 75%, and 100%) transitioning from tensile shear composite to shear. Tensile failure is not only formed by the development of tensile cracks but also by the connection of secondary cracks (shear cracks) and tensile cracks. By defining the initial damage to the rock mass via the elastic modulus, theoretical expressions for the total damage, fracture damage, and load damage are obtained. A damage constitutive model for the rock mass with different fracture penetration degrees is established, and the parameters in the model are given physical meanings (m represents the ductile characteristics of the fractured rock mass, and F₀ reflects its strength characteristics). The deformation and failure laws of the fractured rock mass revealed by the trends of the parameter changes are consistent with the experimental results, indicating the validity of the model construction.</p>