Abstract: To improve the current situation of mine fire in China, and to optimize the deficiency of fire extinguishing technology of the single component inert gas, a dry ice preparation system and a visual test bench for CO₂ phase transformation characteristics were set up. Based on different tube types experiments, the three-phase mixture were prepared, which were composed of liquid nitrogen and dry ice particles, the formation mechanism of three-phase was discussed and the phase transformation characteristics of CO₂ was analyzed by numerical simulation. The result shows that as the included angle of CO₂ pipeline increases, the desublimation temperature decreases from 168 K to 157 K, dry ice desublimation increases. Dry ice particles can be accumulated on the visual inner wall by gravity to form a coating, and its thickness showed a trend of extending to the upper part of the pipeline. The simulation result shows that as the angle between LN2 and CO₂ branch pipe increases from 30° to 90°, the fluid flow rate increased from 14.5 m/s to 15.8 m/s, the temperature decrease-rating increased, and the volume fraction of dry ice at the bottom of the pipe increased, which was consistent with the experiment results.