Abstract: It is unavoidable that the strength of rock specimens is different from each other due to flaw in the rock material. However, the average strength of several repeated testing does not represent the actual property of rock material. In this paper, the complete stress-strain curve of flawed specimen was studied, and a suggestion was made to estimate the "ideal strength" of flawed specimens. The influence of confining pressure on triaxial strength was obtained, which can be used to study the yield and failure of specimen during the process of reducing confining pressure . The distribution of flaw degree of rock material was discussed, and strength criterion was given.