<p>Temperature and thermal damage have a significant impact on underground engineering construction (such as geothermal energy extraction, nuclear waste storage, and post-fire tunnel reconstruction). Laboratory experiments were conducted to investigate the evolution of physical parameters, mechanical parameters, and failure characteristics of rock under different thermal treatment temperatures (<i>T</i>) and confining pressures (<i>σ</i>₃). The research results indicate that when <i>T</i> exceeded 600℃, the density and mass of the rock samples decreased more significantly. As <i>T</i> increases, the peak strength and elastic modulus decrease linearly, while the peak strain, Poisson’s ratio, and cumulative acoustic emission counts exhibit an exponential increase trend. The macroscopic fracture angle of the rock sample decreases with the rise in <i>σ</i>₃ and <i>T</i>, and the failure mode transforms from brittle tensile to plastic shear failure. As plastic shear strain (<i>γ</i>_p) increases, the cohesion exhibits a trend of first increasing and then gradually decreasing in the form of a normal function, while the internal friction angle follows an exponential function relationship with <i>γ</i>_p. Temperature and confining pressure both have a significant constraining effect on the dilation angle. Based on statistical damage theory and microscopic element assumptions, the constitutive relationship between stress and strain for thermally damaged rocks was derived, and the intrinsic connection between damage variables and the confining pressure and heat treatment temperature was established. The theoretical stress-strain curve of thermally damaged rock was compared with the experimental results, validating the accuracy of the model. The results are expected to reveal the deterioration mechanism of rock induced by high temperature and provide theoretical guidance for stability assessment of underground engineering.</p>