Abstract: Permeability is the key factor of coal bed methane(CBM)development.The concept "dynamic permeability" has been widely recognized in the development of CBM.The solid-gas coupling model is established based on the basic theory of solid-gas,the definition of porosity,which used volumetric strain as transfer variable and comprehensively considered the effect of adsorption expansion and Klinkenberg on the coal.This thesis sets an example of the single bedding boring gas extraction in the coal mine in Shanxi Province,and combines with coal seam characteristics of the research area and the COMSOL Multiphysics software to carry out numerical calculation.Consequently,the effective radius of 3^# coal seam with bedding boring extraction gas is obtained,which with the actual situations to optimize the arrangement of gas extraction drilling hole.Ultimately,the drainage rate(25%-30%)of fully mechanized caving face in safety production is ensured.Not only for great extraction effect,but also for saving the project cost.