Based on the CT image of rock, we come up with a new method of CT image analysis and make the best use of information of CT images. Accomplish reinforcement of CT image of rock according to regulating contrast of CT image. The real microstructure, cranny and hole could be extracted through the technique of image segmentation. On the basis stated above, Marching Cube algorithm is applied to conduct a 3D reconstruction of successive CT tomographic images, visualization is implemented on rock cracks distribution during different damage stages, In this way we can get not only the directly visual course of damage propagation but also a digital representation of the actual spatial distribution of different materials in the rock. And we define the damage variable about damage volume and obtained the relation between damage variable and damage deviatoric stress which correspond exactly to the damage propagation characteristics. Lastly, we calculate the box counting dimension of the rock sample, and through observation of the dimension curve, we summarize the changes of rock damage under stress.