Abstract: To study the evolution law of permeability parameter of pressure-bear broken coal,the permeability evolution experiments of coal samples with different particle sizes under different axial pressures were carried out using the self- designed experimental device for the coal permeability evolution. The experiment results show:① Under the same pressure,with the increase of coal sample particle,the permeability became smaller gradually,and the permeability of large range of coal sample particle was small. Under the same pressure increment,with the increase of coal sample par- ticle,the permeability change rate became bigger gradually,and the permeability change rates of big mixed particle were higher than the change rates of single particle or small mixed particle. ② In the lower pore pressure range,the permeability of coal samples showed a decreasing trend with the increase of pore pressure,and there existed a critical value of axial pressure (about 9 MPa). When the axial pressure was less than the critical value,with the increase of pore pressure,the permeability changing trend of coal sample was more obvious;and when the axial pressure was greater than the critical value,the permeability changing trend was more gentle. ③ At the beginning of loading,with the decrease of the porosity,permeability declined approximately linearly;when the axial pressure was to 9-12 MPa,and the permeability decreasing trend was gentle relatively;continuing to increase the axial pressure,the permeability de- creased sharply.