The uniaxial and conventional triaxial compression tests were conducted on granite from Sanjiang region of Yunnan-Tibet railway in the laboratory. The deformation characteristics and the damage evolution law of rocks were examined under different confining pressures. The results show that the internal cracks experience five stages during the compression deformation process

including no crack

crack initiation and stable propagation

crack accelerating propagation

crack decelerating propagation and crack termination. In addition

confining pressure significantly influences deformation characteristics of rock. Based on the above analysis and the damage model of micro units

a damage constitutive model is developed under the triaxial compression condition. The proposed model has a simple function form and distinct physical meaning parameters

which can be used to describe both the pre-peak and post-peak deformation characteristics of rocks. Furthermore

theoretical results obtained by this model are in good agreement with experimental results in the literature. The rationality of the model is verified by the parameter analysis.