Abstract: To investigate the competitive adsorption mechanism of ternary gas,the effects of CO2 storage and restrain degree of O2 adsorption after the different proportions of power plant flue gas injecting into the gob,the coal structural model is constructed,and the competitive adsorption behavior of CO2 ,N2 and O2 is simulated using Grand Canonical Monte Carlo method at special temperatures and pressures with the condition in gob to conduct flue gas injecting. The results show that the adsorbed amount of N2 and O2 decreases,and the adsorbed amount of CO2 and the total adsorbed amount increases with the increase of flue gas proportion,but the rates of decreases and increases slightly reduce. While the coefficient of variation of isosteric heat is only 0. 48% -1. 39% along with the changes of flue gas propor- tions. The adsorptive selectivity of CO2 / N2 and CO2 / O2 decrease with the increase of flue gas proportions,thus the competitiveness of CO2 is weakened. The preferential adsorption sites of CO2 are between -34 and -30 kJ / mol and CO2 turns to secondary adsorption sites after the primary ones are filled in. So adsorbed amount cannot directly reflect from adsorption ability,it is mainly guided by the concentration of components in gas phase and influenced by the com- petitiveness and adsorption sites at the same time.