The failure damage of granite under axial load are caused by the propagation and coalescent of cracks at mesoscale, so it is of important theoretical value and practical significance to to understand the mechnical properties of rock by experimental research on meso damage of granite. The microfracturing process of the pre-crack marble sample on surrounding rock in immerged Long-big tunnel in Jinping Cascade II Hydropower Station under uniaxial compression is recorded by using the testing scheme. According to stereology theory, the propagation and coalescent of cracks at meso-scale are quantitatively investigated with digital technology. Therefore, the basic geometric information of rock microcracks such as area, angle, length, width, perimeter, is obtained from binary images after segmentation. The results show that the new meso-mechanical testing scheme on rock meso-damage could be used to quantitatively analyzed from the geometric information of rock microcracks.