Abstract: To investigate the effect of coal particle size on spontaneous combustion characteristics, this study focuses on the No.9~15 coal seam in the Liuhuanggou Coal Mine. Four coal samples with different particle sizes (0~1 mm, 1~3 mm, 3~7 mm and 7~10 mm) were prepared for temperature-programmed experiments. By real-time monitoring of the gases released from coal samples of varying particle sizes during the oxidation heating process, the critical temperature values of the indicative gases (CO, C₂H₄ and C₂H₂) for spontaneous combustion in the No.9~15 coal seam of the Liuhuanggou Mine were determined. Corresponding models were established, and curve-fitting equations were analyzed. The results show that smaller coal particles have more sufficient contact with oxygen, making oxidation reactions more likely to occur. Gas generation begins earlier, and the concentration increases more rapidly with temperature. The temperature at which indicative gases are produced can be used to predict the oxidation stage of coal spontaneous combustion. These findings offer significant practical value for coal mine safety production and contribute to the risk reduction of coal spontaneous combustion.