To accurately obtain the infrared radiation characteristics of an unmanned aerial vehicle (UAV), its infrared radiation luminance was measured with medium- and long-wave infrared thermal imagers of 3.7–4.8 .m and 7.7–10.3 .m, respectively, and the atmospheric transmittance and atmospheric radiation during measurement were calculated with the MODTRAN atmospheric radiation transmission software. The measurement results show that under these conditions, the radiation of the UAV fuselage skin is weak, the radiation brightness is close to the ground and background radiation brightness, and the radiation brightness is essentially the same in all directions. The radiation brightness of the fuselage skin in the long-wave band was approximately 280 times that of the corresponding part in the medium-wave band. The engine radiation brightness was much higher than that of the fuselage skin. For reasons such as fuselage shelter and structure of the body, the engine radiation brightness is directional, and the radiation is strongest in the backward direction.