There is usually difference between gas measuring permeability and liquid measuring permeability, particularly in low permeability reservoirs. Hq, Zb and Hs of the gas permeability and liquid permeability were measured by experiments in the Ordos Basin. The results of experiment show that the lower the permeability was, the bigger the gap between the gas permeability and liquid permeability was. The gap of the oil measuring permeability and gas measuring permeability was obviously different among tight reservoir, superlow permeability reservoir, ultralow permeability reservoir and low permeability. Therefore the result could be used as a demarcation to divide reservoir. The gap of gas permeability and oil permeability had a great relation to the clay mineral, wettability and surface area to the volume ratio.