The permeability of coal-bed methane reservoirs is the key parameter which reflects the permeation performances of the fluids(gas and water etc.) in the coal seam and decides the migration and production of the coal-bed methane.From in-situ stress,effective stress,embedding depth of coal seam and pressure in original reservoirs,natural fracture and the variations of pressure,the paper analyses discusses the factors affecting permeability rate of coal seam by using the theory of coal petrology,and draws conclusions that there are relativity between the permeability of coal seam and in-situ stress,effective stress,the permeability of coal seam reduces with the increasing of embedding depth of coal seam and the increasing of pressure in original reservoirs,the developed natural fracture is advantageous to increasing the permeability,and the permeability of coal seam is influenced by Klinkenberg effect,substrate shrinking and effective stress during exploiting coal seam.This provides scientific basis for forecasting the permeability of coal-bed methane reservoirs.