Abstract: Measured ventilation resistance and isobar in mining areas,the leakage rate in intake goaf and the distribution of air leakage in mining areas were determined by instantaneous and steady liberation of trace gas SF₆.Gas concentration and temperature are measured and three oxidation areas in goaf are determined.According to oxidation experiment of coal and in situ measurements,the CO and CO₂ can be produced largely by coal and oxygen combination at ambient temperature and the temperature of coal and rock in goaf can rise 10℃ due to heat produced by coal and oxygen combination.The analysis shows that the conditions of the nitrogen injection modeling can be well satisfied if hydrodynamic similarity is pledged to the model.The research shows that nitrogen injection is noneffective for a 200 m long goaf and that there is a great danger of spontaneous combustion because of air leakage for pillarless mining.It is very important to inject nitrogen at the location of air leakage and to take the measures of blocking leakage and eliminating pressure difference.