Abstract: The control equation of deformation in dual porosity coal seam is established and Biot pore pressure coefficient based on the theory of adsorption in coal seams is identified. The numerical models of coal matrix and fracture permeability were established respectively under the condition of adsorption. By increasing pore pressure of the matrix, matrix volumetric strain will occur and matrix volume bulk modulus will decrease. The increased volume of matrix occupies part room of pore, which results in the decrease of the coal seam permeability. With the adsorption of matrix, after a certain time, coal bed fracture permeability appears steep fall.