The damage and failure of rock under loading are caused by the propagation and coalescent of cracks at mesoscale, so it is helpful to understand the mechanical behaviours of rock by quantitatively investigating on mesostructure of rocks. Based on the theory of damage mechanics, a digital experimental system on rock meso-structure is proposed. In this paper, the digital studies are conducted on the meso-structure of the marble from Jinping, Sichuan with the damage theory. Lots of meso-structure images are obtained through SEM observation. Based on digital image processing theory, some meso-level characteristics of micro-cracks are obtained such as length, azimuth, width, area and circumference. With the statistics theory and the Monte Carlo theory, the meso-level information of micro-cracks and their morphology are simulated in the representative volume element (RVE) of the Jinping specimen.