Abstract: Due to the flammable outburst coal seam working face, large air quantity, goaf float coal spontaneous combustion in Shoushan Mine, in order to prevent severe leakage after nitrogen injection in goaf, we achieve good fireproof effect by diazo fire prevention technology. We introduce the experimental methods and results of oxygen reduction effect, diazo ratio and velocity, and introduce the methods and parameters of working face nitrogen injection, composition of coal mine fire prevention and extinguishing system in Shoushan Mine, and analyze the effect of oxygen reduction, cooling and the inhibition of float coal spontaneous combustion after nitrogen injection in goaf.