Abstract: In order to study the combustion characteristics and combustion efficiency of coal samples with different particle sizes under high temperature conditions, the combustion characteristics parameters of 6 coal samples with different particle size under thermal radiation were measured by cone calorimeter. The results show that the ignition time is positively correlated with the coal particle size. The peak value of heat release rate gradually decreases with the decrease of coal particle size. In the stable stage of the heat release rate curve (>150 s), the heat release rates of coal samples with different particle sizes in descending order is >0 mm to 0.12 mm, >0.12 mm to 0.15 mm, >0.15 mm to 0.18 mm, >0.18 mm to 0.25 mm, >0.25 mm to 0.38 mm, >0.38 mm to 0.83 mm, and the total heat release rate increases gradually with the decrease of particle size. With the increase of coal particle size, the total smoke release increases, and the flue gas generation rate and total smoke release of the coal sample with the largest particle size (>0.38 mm to 0.83 mm) are the largest. The rates of CO and CO₂ generation increase with the decrease of coal particle size during coal sample combustion. The fire performance index(F_FPI) and fire growth index(F_FGI) of coal samples were introduced, and the combustion efficiency of coal samples with different particle sizes was compared and analyzed. The results show that coal sample with the smallest particle size (>0 mm to 0.12 mm) has the highest combustion efficiency. The lowest value of fire performance index (F_FPI) is 0.27 m²·s/kW, and the highest value of fire growth index (F_FGI) is 3.70 kW/(m²·s). The research results have a certain reference significance for revealing the influence of particle size on the combustion characteristics of coal samples under high temperature environment.