NOVELTY - Gas separation of oxygen-containing coal bed comprises separating and purifying methane from e.g. oxygen, nitrogen and methane present in oxygen-containing coal bed gas by performing low-temperature rectification through a rectifying tower for forming the oxygen-containing coal bed gas from which methane is separated and purified, where a triangular area is formed between methane volume concentration, and oxygen volume concentration in a coordinate system, and when the methane volume concentration and oxygen volume concentration enter into the triangular area, possible explosion occurs.    USE - The method is useful for the gas separation of the oxygen-containing coal bed.    ADVANTAGE - The method provides low-temperature cold energy required by the liquefied methane; improves separation and purification of methane; and is safe, simple and easy to operate.    DETAILED DESCRIPTION - Gas separation of oxygen-containing coal bed comprises separating and purifying methane from e.g. oxygen, nitrogen and methane present in oxygen-containing coal bed gas by performing direct low-temperature rectification of the oxygen-containing coal bed gas through a rectifying tower for forming the oxygen-containing coal bed gas from which methane is separated and purified, where a triangular area is formed between methane volume concentration (as abscissa), and oxygen volume concentration (as longitudinal coordinate) in a coordinate system, which is a vertex at a certain temperature and pressure under methane volume concentration explosion lower limit point, the methane volume concentration explosion limit point and methane volume concentration critical explosive point, and when the methane volume concentration and oxygen volume concentration simultaneously enter into the triangular area, possible explosion occurs, i.e., the area is an explosive area. The method comprises adding low temperature working medium at an upper part of the rectifying tower in a proper position, where the low-temperature working medium components, flux and gas-liquid ratio of the gas or liquid of the variable oxygen volume concentration and the methane volume concentration of the rectifying in the process do not simultaneously enter into the explosion area. The low temperature working medium is oxygen mixture, air, oxygen and nitrogen mixture separated from air, or nitrogen-based mixture.