Abstract: The failure damage of granite under cyclic load 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 the meso-damage of granite. A great deal of mesostructural images of Changjiang granite in Hainan Province have been obtained by means of scanning electron microscopy(SEM). The mesostructural images of marble are processed by regional growing theory based on image processing technique. The meso-damage information of granite microcracks are obtained from SEM images. Then, the mesostructural information of microcracks is analyzed by statistical theory and the distribution regularities of microcrack parameters are proposed. Quantitative analyses of meso-damage characteristics under cyclic load are made from minerals and microcracks. It is shown that most of transgranular cracks are mainly concentrated within the feldspars and microcracks are initiated as boundary and intragranular cracks around micas. And the major meso-damage of fatigue damage is intragranular cracks. The energy of the development of transgranular cracks and intragranular cracks account for most of the micro-crack initiation energy consumption

Key words: cyclic load, quantification, mineral crystal, microcrack