Abstract: At medium and low confining stress of triaxial and uniaxial compressive load, five stages as being (1)crack closure, (2)linear elastic deformation, (3)crack initiation and stable crack growth, (4)critical energy release and unstable crack growth, and (5)failure and post peak behavior can be defined for brittle rock material. Direct observation on the surface of flaw contained specimens, indirect observation techniques such as strain monitoring, Acoustic emission(AE)monitoring, acoustic wave velocity monitoring, computerized tomography scanning, microscopic observation(SEM/ESEM)etc, . Under the compressive load, tensile cracks are the first and primary cracks, which propagate generally along the loading direction. A continuing measure method for acoustic wave velocity measurement during cracking processes of rock was proposed based the discipline of crack propagation. The method will benefit for the indirect observation of cracking processes by monitoring the changes of acoustic wave velocity.