Abstract: As for the situation that it is difficult to extinguish fire after spontaneous combustion in coal mine, adopting the method of sealing fire zone, but it is prone to spontaneous combustion as fire zone unsealed, so crossing point temperature method is used to study the reasons. Different quality of coal samples are tested to get crossing point temperature under best quality coal sample, and different oxidation temperatures are used to get the changes of cross point temperature after cooling for initial oxidation, and then re-oxidation. Combined with infrared analysis, it deduces that the active groups in the center of coal fire will react completely after the coal spontaneous combustion, so it is difficult to spontaneous combustion again, but, the coal that is away from the center point affected by the heat will change the physical and chemical conditions, coal samples is prone to adsorb oxygen and transfer heat, and easy to spontaneous combustion. when the sealing fire zone opened, it is important to pay special attention to the coal spontaneous combustion which is away from the coal spontaneous combustion center, to prevent the spontaneous combustion of coal.