Abstract：The damage structure and constitutive relation of common bedded composite rock are researched. The micrcoscopic study of rock by SEM shows the characteristic of their microstructure and micropore. The damage constitutive equations and damage evolution equation in three dimensional nonlinear state are derived under different conditions，such as unequal biaxial stress，different effective stress，different mechanical parameters and damage evolution processes for every stratification. The study results are well testified by experiments.
