The use of inhibitors to prevent coal spontaneous combustion is one of the common fire prevention and extinguishing technologies used in coal mines at home and abroad. In order to prevent coal spontaneous combustion in Guotun Coal Mine and seriously affect coal mine safety production, selecting the most common halogen salt inhibitor magnesium chloride which had  its concentration of 20%, through the temperature rise test and infrared test after the experimental coal sample is subjected to inhibitory treatment and passed the procedure the macro and micro parameters of the original coal sample and the inhibited coal sample of Guotun Mine during the spontaneous combustion process were studied. It is found after MgCl2 inhibitor is added, the active groups on the coal surface which are fatty hydrocarbon side chain (-CH3 And -CH2) and the content of oxygen-containing groups C=O are significantly reduced, the rate of oxygen consumption during coal spontaneous combustion and the production of CO gas are reduced, and the inhibition rate is reduced in the later period. In this  study, the mechanism of the halogen salt inhibitor from the physical and chemical perspectives. The test results can provide the relevant basis and reference for Guotun Coal Mine to effectively prevent and control underground fires.