Abstract: To achieve precise regulation of low-altitude micro/miniature unmanned aerial vehicles (UAVs), it is essential to obtain the effective detection range of infrared detection systems against UAVs and define the boundaries of infrared systems detection capabilities. Firstly, considering that the UAV's image can not cover a single detector pixel, a theoretical model for calculating the detection range of infrared detection systems against point targets is improved. Secondly, an experimental measurement system is constructed, utilizing an infrared thermal imager and a multi-channel temperature tester to measure the radiative and physical temperatures at multiple surface points of the DJI Air 2S under varying continuous flight durations. These measurements enable the determination of the thermal equilibrium temperature of the UAV during flight. Thirdly, a three-dimensional geometric model of the UAV is developed, and the radiative intensity in the 8~14 μm wavelength band is numerically calculated using the Monte Carlo method. Finally, based on the established detection range model, the spatial distribution of the detection range for the thermal imager against the UAV is numerically simulated across different detection angles. To validate the theoretical results, experiments are conducted to measure the practical detection range. Comparing the detection ranges derived from numerical calculations and experimental measurements under identical viewing conditions, the relative error between them is within 10%. It demonstrates the rationality and reliability of both the detection range model and the numerical simulation methodology.