Abstract: In order to master the concentration distributions and diffusion laws of various components of gas in goafs, study their changes with time and obtain the reasonable parameters of goaf sealing and inerting fire-fighting technology, the concentrations of various components of gas during inert gas injection were monitored by using sampling and experiment analysis methods. Then the process of sealing and inerting in the goaf was simulated based on the permeability and diffusion theory with Fluent software. The simulation results are essentially coincident with the measured data, validating the accuracy of the simulation results. It is also found that a "Double U" ventilation system can make the airflow field distribution uniform in the goaf. The concentrations of O₂, CO₂ and N₂ gradually reduce with the increase of distance from the working face while the concentration of CH₄ radially increases from the center of the lower corner under the normal ventilation case. The concentrations of O₂ and N₂ gradually increase over time as the inert gas injection process go on, but the concentrations of CH₄ and CO₂ decrease at the same time.