Abstract: Low-temperature oxidation may occur during coal storage, which will reduce the quality of coal, and if the coal spontaneous combustion occurred, it may cause greater heat loss. In order to deeply study and analyze the micro-structural change of coal in its storage process, coal pile storage test was conducted in Jiangyou Power Plant, coal samples were regularly taken and then tested by infrared spectrum in the laboratory. Through the analysis on the infrared spectrum and differential spectrum of the coal samples, it was found that the number of functional groups such as -CH₃, -CH₂- and -CC- decreased, the number of the functional groups such as the alcohol, phenol, ether and ester and the radical group such as -OH increased, and the macroscopic phenomena in the process of the coal pile storage was explained by differential spectrum analysis results. The porosity of coal pile can be reduced by layered compaction during its storage and in the meantime the monitoring should be strengthened so as to prevent the low-temperature oxidation and the spontaneous combustion of coal piles.