Abstract: The permeability and gas-bearing property of coal reservoir are remarkably affected by its thickness. The thickness of the coal reservoirs in the Morth China plots their pemeability in different two pat terns, that of the structurally-destroyed coal reservoirs is negatively related to the well-tesing permeability in tendency, but there exist two relationships with reverse trends in the coal reservoirs with completely-original structure taking 0.5 mD permeability as a threshold value. The coallbed methane content in some area of China shows the increasing pattern with increasing thickness. The threshold permeability of the commercially valuable coal reservoirs in China should be seemingly defined as 0.5 mD or so.