Abstract：In order to probe the effects of high confining pressure and high hydraulic pressure on the marble characters of strength，deformation，brittle-ductile transition and rupture，and damage degradation，the triaxial compression contrastive tests of marble specimens，which are collected from surrounding rocks of diversion tunnel in Jinping hydroppwer station Grade Ⅱ，are tested respectively under three different states of high hydraulic pressure，and high and low confining pressure. Then the microtest (SEM) is carried out to study its microcosmic character of failure surface under three different pressure cases. The test results indicate that under low confining pressure Moore strength line is linear，whereas nonlinear under high confining pressure. The existing of high hydraulic pressure constrains the development of brittle-ductile transition，reducing the strength and intensifying fission cracking in soften area. Based on the testing analysis of microcosmic digital image，there are smaller fissions，higher density and even distribution under high confining pressure than under low one. Microcosmic damage mechanics of rock cracking under high confining pressure and hydraulic pressure is given. Reliable testing basis is offered to analyze further failure and stability of the noncircular cave surrounding rock under high confining pressure and high hydraulic pressure.
