A meso-mechanical testing scheme based on scanning electron microscopy(SEM) is developed to carry out the experiment of microfracturing process of rocks. The microfracturing process of the 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 digital image processing theory, the meso-structural information of rock microfracture such as length, angle, area, etc are obtained from SEM images. Then, the meso-structural information of microfracturing process under uniaxial compress is analysized and the distribution regularities of microfracture parameters are generalized extreme value distribution with variable parameters. The process was described of the damage from the perspectives of macro-and micro-scale under the uniaxial compression loads.