Abstract: In order to study the magnetic changes of coal-rock mixtures after high-temperature baking, it provides effective guidance for the application of magnetic methods in the delineation of fire zones. The magnetic susceptibility measurement system was used to determine the Nalinmiao coal. The magnetic susceptibility of coal-rock mixed samples mixed with different proportions of rock was studied respectively. The influence of temperature, particle size, magnetic field strength and coal-rock ratio on the magnetic susceptibility of the samples were studied. The results show that the magnetic susceptibility of the burnt coal-rock mixed sample formed in the whole range of normal temperature to 600 ℃ increases with the increase of temperature and decreases with the increase of the external magnetic induction intensity. When the baking temperature is less than 400 ° C, the smaller the particle size of the sample, the greater the magnetic susceptibility; the effect of high temperature baking on the composition and structure of the rock is analyzed by X-ray diffraction experiments, indicating that during the high temperature baking of the rock, Increased hematite and pyrite content is the main cause of increased susceptibility which is the main reason for the enhanced magnetic properties of sintered rocks compared to room temperature rocks. Finally, the GEM system company's GSM-19T proton magnetometer was used to detect the fire area in the key area of Nalinmiao Coal Mine No. 2 shaft. The comprehensive analysis was used to determine the suspected fire area, and the borehole temperature measurement was used to verify the magnetic detection. Fire zone reliability.