Abstract：Generation and development of micro-crack in carbonate rock will affect its mechanical characteristic obviously. Based on triaxial test and stereoscan photograph of carbonate rock consisting of dolomitic rock，limestone，dolomitic limestone，the relationships between stress and strain are divided into tightening phase，linear elastic deforming phase，generation and development of micro-crack phase and fracture phase. Corresponding to these four phases，the change of micro-crack shows the close of original micro-crack，stably sustained linear elastic deforming，new micro-crack generation，expanding and stably developing，and integral breaking. The experiment shows that the micro-crack begins from off-lying to circum of the pore in compression，and then to the pore and rock collapse. The development of micro-crack begins from separation fracture to shear fracture，then to occurrence of separation fracture tracking shear fracture，until fractures are penetrated. The separation fracture and shear fracture are included in initial micro-crack of carbonate rock. The rock fracture begins at the end of micro-crack，which is the stress concentration position after loading. Right round fault，contact point of grain boundary and the micro-crack density increase because of stress concentrating highly. The fracture generates when the stress reaches or approaches to the peak value，and then，crack and strain softening occur successively.
