In view of the problem where there is abnormal continuous CO exceedance in the tailgate corner without any sign of spontaneous combustion associated with the mining of low metamorphic coal seam, both desorption experiments and ambient temperature oxidation experiments were carried out, and the ambient temperature oxidation characteristics and its mechanism were studied. The results demonstrate that the original coal seam from which the experimental coal sample was taken, does not contain CO and CO2, and the coal sample can oxidize at ambient temperature. The O2 consumption rate, CO and CO2 production rate is not directly related to the particle size. Low O2 concentration can inhibit but not eliminate the ambient temperature oxidation. In addition to the active sites of coal itself, the ambient temperature oxidation reaction rate is also affected by the inhibitory substances produced by the reaction itself. R1(���CO/���O2), R2(���CO2/���O2) and R3(���CO/���CO2) indexes are mostly not affected by the changes of particle size, O2 concentration and oxidation rates, and the ambient temperature oxidation of coal is dominated by a single mechanism. The ambient temperature oxidation mechanism is also theoretically deduced. The research will have important significance for controlling the abnormal exceedance of CO.