Abstract: Magnetic anomaly is an important geophysical feature of coal field fires. In order to study the magnetic change law of high-temperature heated rocks and provide effective guidance for the application of magnetic method in the delineation of fire zones, the susceptibility measurement system was used to determine the magnetic susceptibility of Nalinmiao 3-1 coal roof sandstone. The effects of temperature, particle size, and magnetic field strength on the magnetic susceptibility of the samples were studied. The results show that the magnetic susceptibility of the burnt rock in the whole range of 25 ℃ to 600 ℃ increases with the increase of temperature, and decreases with the increase of the external magnetic induction intensity. When the heated 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, FeCO₃ is oxidized into Fe₃O₄, which is the main reason why burnt rock is more magnetic than normal rock.