Abstract: To study the characteristics of coal with different particle sizes in the process of oxidation and spontaneous combustion, differential scanning calorimetry (DSC) was used to study the lignite from Chahasu Coal Mine, Inner Mongolia. The influence of coal particle size on the peak and critical characteristic temperature under different heating rates was studied, and the activation energy was quantitatively analyzed. The results show that the peak temperature and critical temperature of coal decrease with the decrease of particle size under the same heating rate. The peak temperature, critical temperature, and peak area of coal with the same particle size increase with the increase in heating rate. In the range of less than 0.50 mm granular coal sample, the larger the particle size, the higher the critical temperature corresponding to the larger heating rate; the Arrhenius formula method is used to solve the activation energy of coal samples. The change rate of heat absorption of coal samples with 0.15-0.25 mm particle size is the largest and the activation energy is the smallest. The coal in this particle size range needs the least energy to reach the activation state, and the possibility of spontaneous combustion of coal samples is the largest.