NOVELTY - A raw gas of oxygen-containing coal bed gas is cooled, and the oxygen-containing coal bed gas is rectified, to obtain purified-and-separated methane. The purification and separation process further involves detecting initial volume concentration of methane within raw gas, plotting a coordinate by taking volume concentration of methane as abscissa and by volume concentration of oxygen as ordinate, and determining explosion triangle of coal bed gas under initial state, removing oxygen from raw gas, controlling methane volume concentration, and separating methane from raw gas.    USE - Method for purifying and separating methane from oxygen-containing coal bed gas.    ADVANTAGE - The methane is safely and economically separated and purified under reduced explosion conditions.    DETAILED DESCRIPTION - A raw gas of oxygen-containing coal bed gas is cooled, and the oxygen-containing coal bed gas is rectified, to obtain purified-and-separated methane. The purification and separation process further involves detecting initial volume concentration (y0) of methane within the raw gas, plotting a coordinate aiming at oxygen-containing coal bed gas during separation by taking volume concentration (Y) of methane as abscissa and by volume concentration (X) of oxygen as ordinate, and then determining explosion triangle of oxygen-containing coal bed gas within the corresponding coordinate under initial state, removing oxygen from the raw gas, controlling volume concentration of methane, and separating methane from the raw gas. The oxygen removed from raw gas is cooled when y0 is located in oxygen short region of the coordinate region of oxygen-containing coal bed gas. The quantity of removed oxygen is measured by satisfying relation: X greater than or equal to (((y0) of oxygen)(100-yc)-(yc of oxygen)(100-y0))/((y0 of oxygen)(100-yc)-(y0yc of oxygen)), where X is molecular ratio between removed oxygen and raw gas, y0 is initial volume concentration of oxygen within the raw gas, yc is volume concentration of methane at critical explosion point within the coordinate region corresponded to the most explosive point during separation, and yc of oxygen is volume concentration of oxygen at critical explosion point within the coordinate region corresponded to the most explosive point during separation.