Abstract: Spontaneous combustion in coal gangue piles is a common hazard during coal mining, causing atmospheric pollution and heavy metal leaching, and further endangering the safety of surrounding residents. This study focuses on a spontaneously combusting coal gangue pile in northern China. A method for delineating hazardous fire zones based on radon concentration was developed and validated through field application. Data on surface radon concentration, temperature, CO, CH₄, etc., were collected using a 20 m×20 m grid. Radon concentration contour maps were generated using Kriging interpolation. Anomaly thresholds were determined by combining traditional statistical methods and fractal methods. The location method for spontaneous combustion area of coal gangue mountain based on "spatial interpolation prediction - anomaly threshold determination - anomaly zone identification" was established. Meanwhile, the criteria for determining the characteristics of coal gangue volcanic areas were established, and a comprehensive criterion for the fire area range, burial depth and oxidation degree of coal gangue was formed with radon concentration, temperature and index gas concentration as indicators. The dangerous area of coal gangue fire area was accurately located, and effectiveness of the method was verified by combining the field drilling temperature and index gas concentration data. Results show that the distributions of radon concentration and temperature follow a normal distribution. Thirteen radon anomaly zones and four temperature anomaly zones were delineated, four of which were identified as severe oxidation zones. Using a depth index (I_D = normalized radon concentration index + normalized temperature index), the fire depth was categorized as shallow (0–2 m), medium (2–7 m), or deep (>7 m), and the oxidation degree was classified as slow oxidation (Stage II_O) or in-tense oxidation (Stage III_O). Validation using 13 boreholes revealed that radon anomaly zones were highly consistent with high-temperature zones (≥120 ℃) and areas of high CO concentration (≥1 000×10⁻⁶). This method provides a scientific basis for the comprehensive determination of fire zone extent, oxidation intensity, and burial depth in coal gangue piles.