Based on research results of composite material and continuum damage mechanics theory

a three-dimensional anisotropic damage model was presented. To describe the damage evolution of rock material during loading/unloading

the derivate eigenmodes in the proposed model are assumed to be related with the uniaxial behavior of the rock material. Each eigenmode has a corresponding damage variable due to the fact that damage is a function of the magnitude of the eigenstrain. Within an eigenmodes

different damage variables can be used for tension and compression. Hence

these damage variables in six eigenmodes can form a 4th rank symmetric damage tensor which stipulates evaluation of effective elastic modulus of the rock material with microcracks and an adequate description of the evolution of damage.In this model

the tensor decomposition technique is employed. It means that the stress and strain tensors are decomposed into six eigentensors

which correspond to six eigenvalues accordingly. The stress-strain curves for different directions

which can be obtained from the experiment

are assumed to be different in each normal eigenmodes.This model was also developed into finite element code in explicit format; and the code was integrated into the well-known computational environment ABAQUS using the ABAQUS/Explicit Solver. Numerical simulation of an uniaxial compressive test for a rock sample is used to examine the performance of the proposed model. The results of the numerical simulation show that it is possible to reproduce most of the observable characteristics of anisotropic behavior and damaged zone in rock materials.