Abstract: The continuous slow burning of underground coal fire is the result of coal smoldering propagation effects. A self-designed similar experimental platform was designed and built in order to explore the propagation characteristics of vertical forward smoldering of coal fire, and the simulation experiment of vertical forward smoldering of long-flame coal was carried out under different air supply rates, and the effects of the air supply rate on the real-time change of temperature, the maximum reaction temperature, the total length of smoldering and the combustion rate of four measuring points in the smoldering propagation direction of coal were analyzed. The results show that, in the vertical forward smoldering process, the coal goes into the evaporation stage of constant temperature at 80 ℃~85 ℃ range, the temperature rising fast, then in turn into the volatile and carbocoal/coke burning off stage. Under the condition of 2, 0.8 m³/h supply air volume, the top coal body caved to the bottom during the smoldering process, while the supply air volume under 0.4, 0.2 m³/h and below did not form obvious collapse. There is an exponential relationship between the length of total smoldering and the airflow rate of coal, and the combustion rate increases linearly with the increase of airflow rate.