Abstract: In order to study the variation characteristics of the gas permeability of raw coal sample in loading-unloading process and negative pressure, on the basis of the three axis seepage experiment instrument, a fluid-solid coupled triaxial stress seepage experimental device is developed. the experimental results show that: under same confining pressure, axial pressure and gas inlet pressure conditions, with the increase of loading negative pressure , the gas permeability of raw coal increased; confining pressure, pumping negative pressure and gas inlet pressure kept constant, the gas permeability increased with the increasing of axial compression, after the maximum, gas permeability reduced with the increase of axial pressure, axial pressure is unloaded to zero gas permeability increased gradually. However, It is difficult to restore the initial permeability, It may be related to the plastic deformation of coal; under high stress, improving the air inlet and outlet pressure to improve gas permeability has little effect.