Abstract: This paper presents analytical results of composition and microstructure of the discrete structural surrounding rock mass in a low geostress region. Rock samples, taken from the surrounding rock mass at different locations of the underground excavation for a water conveyance project, are analyzed for chemical composition, average percentage of content, and microstructures by using electron diffraction and electron-scan microscope. The micro-deformation of the rock is then characterized, thus providing guidelines for further study for macro deformation, failure and stability of rock masses in the low geostress region.