Abstract: Overburden separation grout filling (OSGF) technology compacts the fragmented rock mass in the goaf and changes the seepage characteristics and distribution of the “three zones” of spontaneous combustion in the goaf. In order to investigate the range of spontaneous combustion risks of residual coal in the goaf under the OSGF in the 22301 fully-mechanized caving face of the Tunlan Coal Mine, based on a combination of field measurement and numerical simulation, accurate demarcation of the spontaneous combustion “three zones” in the goaf was carried out. A three-dimensional mathematical model of borehole porosity was also proposed to evaluate the influence of different OSGF borehole locations on the goaf airflow field. The results show that the modified three-dimensional mathematical model of porosity can better reflect the gas flow field in the goaf after OSGF, and the residual accuracy of its simulation results is improved by 22% compared with the field measurement. Compared with the situation without OSGF, the danger of natural ignition in the goaf is effectively inhibited due to the compaction effect after OSGF. Meanwhile, the air leakage flow converges upward, resulting in an increase of oxygen concentration at higher positions in the caving zone of the goaf. The layout parameters of grouting holes will have an impact on the flow field of goaf, and the correlation degree is the spacing of holes, the number of holes and the influence radius of holes.