In order to improve the extraction effect of ultra-low permeability coalbed methane, injecting and drawing industry test of enhanced coalbed methane recovery is carried out by injecting concentration 78% N2 under 850 m depth coal mine of Tianfu Mining Co. Ltd.，in Chongqing. The experiments of free methane emission, vacuum pumping, side injecting and side emission, side injecting and side drawing and intermittent injecting are tested under the condition of single hole and multi holes respectively. The testing results indicate that time-concentration curve of methane drawing is a single peak wave curve which increases and decreases during injecting N2 after reaching the limits of ordinary extraction. The methane concentration of intermittent injecting gas is greater than that of side injecting and side drawing. However, the former declines rapidly and has a shorter migration distance than the latter. The injecting effect of long time side injecting and side drawing is better than that of intermittent injecting. When hole space is 4 m, permeability 1.112×10-4mD, the methane recovery ratio increases to 58.6％ from conventional recovery ratio 52.4% after injecting 5 day. Meanwhile, the seepage flow equation of injecting air is provided and the parameters, such as rational hole mesh space, time and pressure of injecting gas, are simulated. At the same time, application condition and assistant technology about injecting gas are discussed, which provides engineering and theoretical reference to promote the injecting gas technology. Also, the problem of variable definite conditions seepage flow equation is put forward.