<p>Investigating the variations in rock strength and the process of rock failure provides a theoretical foundation for evaluating the safety and stability of underground engineering. To investigate the mechanical response and damage evolution of limestone under triaxial stress in deep engineering, a series of conventional triaxial compression tests were conducted on limestone specimens via the MTS815 electro-hydraulic servo-controlled testing system. Based on continuous damage mechanics and statistical theory, a damage constitutive model was established, which considers residual strength, the coupling effect of confining pressure, and the dependence of the damage variable on confining pressure. The results show that the closure stress, crack initiation stress, damage stress, peak stress, and residual stress of limestone all increase linearly with the increase of confining pressure. The sensitivity of these parameters to confining pressure follows the order: peak stress≈damage stress &gt; crack initiation stress &gt; residual stress &gt; closure stress. The elastic modulus increases with increasing confining pressure, while Poisson's ratio decreases nonlinearly. The failure mode of the specimens is mainly inclined shear failure. The energy evolution process presents distinct stages: slow accumulation—rapid storage—sharp dissipation. Under high confining pressure, the volumetric strain energy and distortional energy required for specimens failure increase significantly, while the proportion of dissipated energy decreases. The theoretical curves derived from the proposed constitutive model are in good agreement with the experimental stress–strain curves, which can effectively characterize the elastic deformation, damage evolution, and post-peak softening behavior of limestone. This study provides an important theoretical basis for the stability analysis and evaluation of deep rock engineering.</p>