Abstract: FLUENT numerical simulation method is used to study the three-dimensional coupled field of goaf. The basic theory of FLUENT fluid numerical simulation software is briefly summarized. Through the self-programming of FLUENT, the development model is used to couple the three-position of the goaf of N3062 working face in Sanmu Coal Mine. The field is simulated and analyzed to obtain the distribution laws of the leakage flow field. Through theoretical analysis, we determine the oxygen concentration reduction value at the boundary between the heat dissipation zone and the spontaneous combustion zone, and then accurately determine the “self-ignition zone” range of the high gassy spontaneous combustion coal seam goaf, further determine range of “spontaneous combustion zone” in goaf by optical fiber temperature measurement system laid in goaf. The accuracy of the flow field distribution in the goaf is verified by the “self-ignition zone” of the measured goaf, and the width of the spontaneous combustion zone in the goaf under different high suction and negative pressure conditions is further simulated, combined with the field measurement of different high suction negative pressure conditions. The change of gas concentration and gas drainage rate in the lower return air passage determines the optimal high suction negative pressure range. Finally, the numerical simulation results of the three-dimensional coupled field in the goaf also show that the “three belts” of the spontaneous combustion show a three-dimensional distribution, and there is a spontaneous combustion danger zone near the rear of the support.