A new apparatus was constructed to investigate the impact of various loading conditions on the permeability of coal specimens. Test results show that loading condition has a definite influence on the permeability of coal specimens. Higher pressures lead to lower permeability, and it seems that the confining pressure has a greater effect than the axial stress does, while the permeability is related exponentially to applied stresses. Based on the experimental results, an equation governing gas seeping through coal seams is deduced within the frame of Darcys Law, which may be helpful to understand the permeability properties of stressed coal seams and to improve the drainage of gassy coal beds.