Abstract: Granite is a kind of surrounding rock in high-level radioactive waste geological repository. Hydraulic characteristics of the surrounding rock directly determine whether or not it can effectively block the groundwater to the direction of nuclear waste repository. The micro cracks structure and chemical weathering is the performance of hydraulic characteristics in surrounding rock. So a quantitative analysis of granite micro cracks and chemical weathering analysis has the certain scientific significance for comparison of the buried depth of high-level radioactive waste geological repository. In this study, seven core samples in different depth of the granite drilling within 600 meters were taken as the research object. The borehole is located in Alxa, Inner Mongolia, China. Using survey grid method and image processing technology, micrographs were translated into binaryzation image of micro cracks. Then, geometric parameters of the micro cracks(such as quantity, width, cranny ratio, etc) were analyzed to describe the spatial distribution the micro cracks characteristics. The morphology characteristics and element content of micro cracks were analyzed by scanning electron microscopy energy dispersive X ray analysis(SEM-EDS).The natural moisture content and CIA are two important parameters of chemical weathering in this study. Finally, Comprehensive evaluation was used to analyze granite integrity. The results show: (1)The complete granite samples' micro cracks development have a general trend from high to low as the sampling depth from shallow to deep in this study area.(2)Fissures are inclined to develop among feldspar and biotite. On the contrary, fissures are more commonly developed in quartz grains.(3)Cranny ratio, average gap width, fracture number and CIA become larger near broken zones.(4)The distance of fracture zone influence on the complete granite can be more than 10.6 m. And the late hydrothermal seepage distance can be more than 50.27 m.(5)Through comprehensive evaluation, 598.8 m underground was the optimum buried depth of nuclear waste disposal repository.