Abstract: Based on the concept of true stress and the strain equivalence hypothesis, a three-dimension elastic-plastic damage constitutive model for rock is established. Combining the nonlinear unified strength model as the yield function and the equivalent plastic shear strain as the hardening parameter considering the effect of stress level, the formulation of elastic-plastic behavior of rock is deduced in the true stress space. As in the normal stress space, the damage evaluation law is given by considering the effect of confining pressure. The present theoretical results and the test data are compared. It is indicated that the proposed constitutive model describes the strength and deformation behaviors and the strain softening behaviors of rock. Furthermore, the model can be employed to simulate rock engineering structures under multi-dimensional nonlinear stress, providing a basic reference for structural design and analysis.