Abstract: The shortest natural spontaneous combustion was an important indicator of natural spontaneous combustion risk evaluation.In order to test the shortest natural spontaneous combustion scientific，it taking 3-1 coal seam of Menkeqing coal seam as studying object，and isolated heat oxidation reaction device was utilized，the production of all kinds gases were test during temperature rise period，and the intersection temperature of 3-1 coal seam was confirmed，and the heat release during oxidation temperature rise period was calculated by chemical bond energy value of CO and CO₂that generated，and the specific heat capacity of coal in different temperature was test on the basis of DSC，and then the lasting time that reached intersection point temperature was calculated partition.The results showed that the natural spontaneous combustion tendency was belong I classification，the shortest natural spontaneous combustion period was 43d，it references for valid fire precaution formulated of coal mine.