Abstract: By establishing the molecular structure model of Pingdingshan bituminous coal（Ｃ108Ｈ71Ｏ4Ｎ）, using the grand canonical ensemble Monte Carlo method, the isobaric adsorption curves of the adsorption capacity at temperature of 298.15 and 303.15 K and the adsorption pressure at saturation and the isobaric adsorption curves of 1 point every 10 ℃ between 10 ℃and 70 ℃ were studied at molecular scale. The results show that the physical adsorption capacity of oxygen is negatively correlated with the equal adsorption heat, and positively correlated with low pressure. Adsorption saturation can be achieved at a certain pressure. The adsorption capacity changes relatively little at normal temperature and pressure. The three-dimensional distribution and energy distribution of the density of physical adsorption of oxygen in coal, the diffusion coefficient of O2 molecule in coal, and the influence of aromatic functional groups and fatty functional groups on the physical adsorption of oxygen are obtained. It is found that pyrrole functional groups have a great influence on the adsorption capacity, so as to intuitively understand the behavior of physical adsorption of oxygen by coal.