Abstract: Liquid CO₂ is more and more used in mine fires in order to further improve the fire prevention and extinguishing efficiency of liquid CO₂. In this paper, a three-dimensional numerical model of goaf is established based on the research background of a working face in Yangchangwan Coal Mine. By changing the injection flow rate, injection time and air speed of liquid CO₂, the influence of CO₂ injection parameters on the cooling range is studied. The results show that the range below 0 ℃ increases with the increase of injection flow rate. When the injection flow rate increases from 2.5 kg/s to 7 kg/s, the range below 0 ℃ increases by 45.7 times, and the range of CO₂ concentration higher than 50% increases by 40 times. With the increase of air speed, the air speed increases from 0.3 m/s to 1 m/s, the range below 0 ℃ decreases by 79.1%, and the range above 50% of CO₂ concentration decreases by 78.9%. Prolonging the injection time can increase the range below 0 ℃. Combined with the air distribution and cooling inerting performance requirements of Yangchangwan working face, it is determined that when the air speed of the working face is 0.5～0.8 m/s, the optimal pressure injection flow of liquid CO₂ is 5～7 kg/s, and the injection duration is 4 ～5 h. The research results provide a theoretical basis for the development of liquid CO₂ fire prevention measures in the working face of Yangchangwan Coal Mine.