Abstract: In order to study the effect of particle size on the thermodynamic characteristics and limiting parameters of coal spontaneous combustion, the oxidation process of coal samples of five different particle sizes (0-<0.9, 0.9-<3, 3-<5, 5-<7, 7-10 mm) was tested and analyzed using the programmed heating system, and the apparent activation energy of the different oxidation phases were determined, and the change characteristics of the limiting parameters of coal spontaneous combustion were quantitatively calculated, so that the mechanism of particle size on the spontaneous combustion of coal could be revealed. The results showed that the apparent activation energy of the coal sample was positively correlated with its particle size, and the average apparent activation energy of coal sample with the particle size of 0-<0.9, 0.9-<3, 3-<5, 5-<7, 7-10 mm is 49.48, 53.56, 57.01, 59.81, 60.83 kJ/mol, respectively. The apparent activation energy of coal sample with the same particle size at different stages is also different, which decreases with the deepening of oxidation reaction, and the apparent activation energy at high temperature stage is lower than that at low temperature stage; as the coal temperature increases, the minimum floating coal thickness and lower limit oxygen volume fraction show a trend of first increasing and then decreasing, while the upper limit air leakage intensity is the opposite; the particle size of coal sample is positively correlated with the minimum floating coal thickness and lower limit oxygen volume fraction, and negatively correlated with the upper limit air leakage intensity. The smaller the particle size of coal sample, the smaller its minimum floating coal thickness and lower limit oxygen volume fraction, and the higher the upper air leakage intensity, the more prone to spontaneous combustion.