Abstract:According to the subarea description theory,the experimental data of sandstone under uniaxial compression test are analyzed. Then the regions of safety,damage and breakage of sandstone are obtained under the condition of the partition thresholds and ,which are equal to 50 and 100,respectively. Simultaneously,the CT numbers in each region are computed. Moreover,the damage evolution ratio and volume strain are calculated,respectively. The damage variables and the information of CT numbers in these spreading regions are obtained. Further,the laws and meso-mechanism of the damage evolution are analyzed. The phase,asymmetry and outburst of damage evolution are also proven. Finally,the existence of determined damage threshold is explained from the view of mechanism.