In order to improve the effect of nitrogen injection of fully mechanized caving face, interval of nitrogen injection pipeline and locations of nitrogen injection are needed to be reasonably settled. Based on air leakage flow field and the change law of gas leakage in goaf, the method of pre-embed beam tube sampler in goaf was adopted, the change of gas composition along with working face advancement determined the scope of goaf spontaneous combustion “three zone”, which was applied in 8102 fully mechanized caving face in Tongfa Dongzhouyao Coal Corporation Ltd.. The result showed that the full mechanized caving face cooling zone was 0 ~ 15 m, oxidation zone 15 ~ 95 m and choking zone more than 95 m.