Abstract: The experimental study on several key factors of coal specimen permeability is conducted herein. Permeability properties of coal specimens are analyzed systematically for different gas pressure, and different stress-strain conditions. Quantitative and qualitative relation between coal sample permeability and confining pressure, gas pressure and stress-strain curve is established respectively. The controlling mechanism and changing laws of permeability of coal samples under variable loading conditions are discussed. The results show that: for fixed gas pressure condition, coal permeability decreases with increasing of confining pressure; and the decreasing law obeys an exponential law; for fixed confining pressure condition, the relation between permeability and gas pressure is show a approximate "V" cure in shape affected by Klinkenberg effect; at the stage of micro fissure closing and elastic deformation, the permeability of coal specimen decreases with the increasing of stress; after entering into the yield stage, the permeability of coal specimen reaches the minimum and the anti-exceeding is accomplished before it reaching the peak strength.