Abstract: Aerial gamma spectroscopy measurement has important application value in mineral geological exploration, environmental radiation monitoring, and nuclear emergency response due to its advantages of high efficiency, flexibility, and avoidance of personnel radiation exposure risks. With the rapid development of drone technology, drones equipped with gamma-ray spectrometers have become a more flexible and cost-effective low altitude measurement method. However, drones typically fly at low altitudes below 40 meters, and complex terrain can significantly affect the solid angles of detection and the attenuation of gamma rays in the air, thereby reducing the accuracy of measurement results. This article proposes a terrain correction method for unmanned aerial vehicle (UAV) gamma spectroscopy measurement based on digital elevation model (DEM) data, targeting typical complex terrains such as mining pits, stepped mining faces, ore piles, and waste rock piles in open-pit rare earth mines. By establishing a micro element detection factor model and combining it with finite element discretization algorithm, quantitative correction of terrain undulations in the detection area can be achieved. The Monte Carlo simulation and field measurement results show that this method can effectively control the gamma ray intensity response error of terrain such as ridges, valleys, gentle slopes, and slopes within 10%, significantly improving the data quality of low altitude drone gamma spectrum measurement. The unmanned aerial vehicle (UAV) airborne gamma spectroscopy measurement in the open-pit mining area of rare earth mines shows that the relative error between the element content measured by UAV airborne gamma spectroscopy after terrain correction in the measurement area and the weighted average element content measured by surface gamma spectroscopy within 90% correction range is within 30% of the number of points, and the uranium content has increased from 53.2% without terrain correction to 74.3%; The thorium content has increased from 80.3% without terrain correction to 93.3%; The potassium content has increased from 94.7% without terrain correction to 97.2%. The terrain correction method has been verified to have strong practicality and reliability.