Abstract: In order to improve the effect of nitrogen injection in large composite goaf of the two-stage middle working face in the fourth level 11 floor of Xing'an Coal Mine, FLAC^3D numerical simulation software was used to carry out stress distribution simulation, and COMSOL software was used to establish a numerical simulation model of nitrogen injection and fire prevention in goaf, and to carry out numerical simulation of nitrogen injection effect. The relationship between coal pillar width and stress distribution and the three zones of spontaneous combustion under different nitrogen injection modes in goaf were analyzed. The simulation results show that non-pillar mining between sections can effectively reduce the coal stress and the risk of rock burst. However, a large area of compound goaf will be formed, which will increase the width of oxidation zone in this goaf and form a reburning oxidation zone in the old goaf. After nitrogen injection, the accumulation area of high concentration nitrogen will be reduced, and the fire prevention effect will be significantly reduced. It is helpful to improve the effect of nitrogen injection by prevent grouting in the old goaf, and increasing the distance of nitrogen injection port and nitrogen injection quantity, borehole pressure injection of nitrogen can be used in the partial incomplete filling area, the fire prevention effect of comprehensive nitrogen injection of non-pillar mining is improved remarkably.