Abstract: Through analyzing the moving characteristic of the original gas in goaf, it obtained the major influence factors affecting the nitrogen injection effect in goaf. Then according to the foundation of the inerting mathematical model about nitrogen injection for fire prevention and extinguishing, it used the FLUENT software to make analytical simulation for the mathematical model, and it verified the results combined with the actual situation of the coal mine site. It studied the influence of the position of nitrogen injection port and the nitrogen injection capacity on the three zones change of goaf.