Abstract: The 3 # coal seam in Shaanxi Nonferrous Yulin Coal Industry Co.,Ltd.,is a “Ⅰ” type coal seam prone to spontaneous combustion, and the pressure of fire prevention and extinguishing in goaf is high.The spontaneous combustion prevention and extinguishing system based on nitrogen injection is established.In order to study the actual effect of nitrogen injection in the field, observation beam tubes are layout along the closed wall of auxiliary transport lane and the return air lane in 30201 working face, and gas parameters in the goaf are collected and comparatively analyzed before and after nitrogen injection.The results of our study show that after nitrogen injection, the oxidation zone range of air inlet side's goaf is shortened to 210～285 m, and the width of the oxidation zone is shortened by about 40 m compared to that of before nitrogen injection.The effect of nitrogen extraction is significant, effectively reducing the risk of coal self-igniting in goaf.