Abstract: Based on the principle of effective stress considering the expansion stress of coal rock, the porosity and permeability of coal reservoir dynamic change model is established considering the effect combination of coal matrix deformation and the effective stress caused by the gas pressure. Combined with stress field equation of coal rock deformation and gas seepage field equation, the multi-physical field coupling model in coal mining area is established. No.3 coal seam of Shanxi group in southern Qinshui Basin is taken as a geological model and Comsol-Multiphysics is used for numerical simulation, the change of pore pressure field is analyzed under the different parameters and different working conditions in the coal seam. The research results show that CBM extraction is mainly influenced by the buried depth of coal seam, porosity and permeability, which is less affected by the negative extraction pressure.