Abstract: In order to study the feasibility that air replace the N2 displacement out coal bed gas, based on the high pressure volume method, the paper had a study on the coal competitive adsorption features of different concentration blended N2-02 mixed gas.The N2-O2 mixed gas competitive adsorption law of the test coal sampl es and the coal adsorption law of 02 in the mixed gas were obtained.The study showed that the coal adsorption constant of N2-O2 two element mixed gas was between the adsorption constant of the single component N2 and 02.With the N2 concentration increased, the adsorption constant would be steadily increased and would be clo sed to the adsorption constant of the single component N2.The coal adsorption value of 02 in the mixed gas would be in a low level, the max adsorption value within th e test scope of the experiment was only 1 mL/g and would not reach the spontaneous combustion limit. The experiment results showed that air applied to replace N2 dis placement out coal bed gas was feasible.