Abstract: The signal parameter of rock's acoustic emission is offractal nature. The signal parameters of acoustic emission areobtained in uniaxial compression experiment about griotte and red sandstoneat different stress levels. By introducing relevant dimensions functions, the dimension number of signal parameters of rock's acousticemission in time domain at different stress levels is computed andthe relevant dimensions are obtained as a function of stress levels. The results show that the process of AE has less obvious fractal featurewith m increasing undersame stress level. Under different stress levels, thedimension number is different, the precess of AE have different degreeof self-similar and fractal nature. Fractal characteristics of theprocess parameter of rock's acoustic emission has a certain dimensionscope.