Abstract: In order to study the combustion characteristics of coal samples with different particle sizes under high temperature conditions, the combustion characteristic parameters of coking coal and its mixed coal samples with particle sizes of 0.200-0.450 mm, 0.125-0.200 mm and 0.097-0.125 mm were tested by cone calorimeter. The combustion efficiency parameters were calculated and the relationship between combustion efficiency parameters and the particle size of coal samples was analyzed. The results show that with the decrease of particle size, the ignition time becomes shorter, indicating that the smaller the particle size of the coal sample, the easier it is to burn; the time required to reach the peak value of heat release rate and the peak value decrease with the decrease of particle size, and the peak value of mixed coal sample is the lowest. When the heat release rate curve tends to be stable, the heat release rate and total heat release increase with the decrease of particle size, and the relationship is 0.097-0.125 mm > 0.125-0.200 mm > mixed coal sample > 0.2000-0.450 mm; the peak value of mass loss rate and the stable mass loss rate increase with the decrease of particle size, and the total mass loss also increases, and the relationship is 0.097-0.125 mm > 0.125-0.200 mm > mixed coal sample > 0.200-0.450 mm. The CO release decreases with the decrease of particle size. With the decrease of particle size, the fire performance index decreases, while the fire spread index increases. The fire performance index of mixed coal sample is the largest, and the fire spread index is slightly higher than that of 0.200-0.450 mm coal sample; the fire risk increases with the decrease of coal particle size, and the fire risk of mixed coal sample is low.