<p>As a result of geological structures and manual excavation, rock masses are subjected to true triaxial stress in underground engineering projects, including tunneling, hydropower stations, and nuclear waste repositories. This stress condition induces anisotropic deformation and damage. Studying the resulting complicated deformation and damage evolution is important for maintaining the stability of a rock mass. In this study, an anisotropic damage model is established to describe the anisotropic damage evolution and constitutive behavior of rock subjected to true triaxial stress based on the statistic damage theory and energy equivalence hypothesis. A second-order damage tensor is defined to reflect the anisotropic damage in the directions of the principal stress; this tensor is dependent on three damage scalars depicting the variation in the elastic modulus and Poisson ratio. Analytical solutions are deduced for two usual loading types in the true triaxial compression tests: constant <i>σ</i>₂ and constant intermediate principal stress coefficient <i>b</i>. The calibration method for the damage parameters is described in detail, and the prediction of the proposed model is compared with the existing models. True triaxial compression tests are performed and adopted to verify the rationality of the model. Good agreement with the experimental results indicates that the model can correctly depict the anisotropic deformation and damage propagation. Finally, the variation and sensibility of the parameters are analyzed and discussed. The accessibility of the damage parameters enables the method and conclusions to be widely applied in underground engineering.</p>