Based on the engineering background of 15206 fully mechanized caving face in Shanxi Pingding Huineng Coal Industry, aiming at the problems of abnormal high CO concentration in the mining process of No.15 coal seam and the unknown dangerous area of goaf under the condition of gas drainage, the numerical simulation method is used to analyze the distribution law of ' three zones ' of spontaneous combustion in goaf, and the dangerous area of fire prevention and extinguishing in goaf under the condition of gas drainage is delineated. The results show that due to the influence of air leakage in high and low gas drainage roadways, the width of oxidation heating zone on the inlet and outlet sides is similar ( 59~62 m ), which is significantly larger than that of conventional working face. With the increase of air supply, the oxidation heating zone moves to the deep and the range expands, and the appropriate reduction of air volume can reduce the dangerous area. The oxygen of the floating coal at the top of the support is sufficient, and CO has been detected locally, which has the risk of spontaneous combustion.