The operating range parameter of an infrared system is an important index for characterizing its imaging performance. At present, there are many methods to calculate the operating distance of infrared systems, but they all have their own applicability and limitations. It is necessary to consider the influence of various factors on the operating distance under different conditions. In this study, based on the detection energy, noise equivalent temperature difference (NETD), and contrast, we found limitations under different conditions. When the observation target was a human, the calculated operating distance based on the NETD model was 8.74 km, which is closer to field experimental data. When the observation target was an aircraft, the calculated operating distance based on the energy model was 32.04 km, which is also closer to field experimental data. These results show that, according to the different characteristics of the target, selecting the appropriate calculation method for the operating distance is helpful in improving the accuracy of the system operating distance estimation.