Abstract: Through the permeability experiment of coal with different coal structure under triaxial stress condition, combined with gas production condition of coalbed methane wells, the coal permeability change laws in drainage process are analyzed. The research results show that coal permeability increases firstly, and then decreases with the drop of pore pressure in a certain axial load and confining pressure. Due to the small mechanical strength of soft and low permeable coal seams, breakage of coal particle between intergranular pore closed sharply with the water level drops in earlier phase, these cause coal permeability decrease greatly; and cause coal permeability improvement more slowly by coal matrix contraction effect than that of the original coal seam structure. The study suggests that staged pressure control and steady pressure relief should be adopted in coal bed methane wells, in that it can keep the coal reservoir fracture and pore opening in a certain degree, ensure the coal bed methane desorption fully, resist the deformation of coal matrix, increase the supply area and improve gas production.