Abstract: The plume is the main portion of the infrared radiation source for the high-altitude and high-speed UAV. To calculate the infrared radiation released from the plume of the high-altitude and high-speed UAV, a numerical simulation of the flow field for the plume of the UAV was firstly performed by using the software Fluent. And, according to the shelter theory of fuselage and the simple spectral band model theory SLG including the Lorentzian-broaden effects and the Doppler-broaden effects of the spectrum, the infrared radiation released from the plume of the high-altitude and high-speed UAV was calculated. Secondly, based on the method of slantwise route equivalent transport, the atmospheric transmittance of infrared radiation was computed. At last, infrared radiation intensity released from the plume of a high-altitude and high-speed UAV was calculated and analyzed after atmospheric attenuation under different work conditions of engine and at different azimuth and observational elevation. At the same time, the impact of pitch angle on the infrared radiation intensity was also analyzed.