The correlation dimension evolution characteristics of acoustic emission(AE) time-series during the instability and failure of coal with and without gas are analyzed base on fractal theory. The results show the coal rock’s AE time-series of deformation stages have obviously fractal characteristics under uniaxial loading. The processes of AE of deformation have different self-similarity, and the correlation dimension can describe the mechanical state of coal. During the triaxial loading process, the stress-varying trend of AE time-series of coal with and without gas is similar to the trend of AE correlation dimension. The sharp decrease of AE time-series’ correlation dimension can be considered as a “precursor” for failure. This feature doesn’t change with the change of confining pressure and gas pressure.