Plume is the main infrared source of a long-endurance UAV,and its infrared radiation numerical calculation is very important for calculating the infrared characteristcs of the whole UAV.This paper built the geometrical model of the flow field structure of UAV plume by analyzing the characteristcs of the flow structure.And,The temperaturre field distribution of the UAV plume was calculated based on the eddy current propagation theory.And then,spectral infrared radiation characteristics of the UAV plume at 2-5μm were obtained by the single band C-G approximation method.The results show that the temperature in the core area of the UAV plume is higher,and the infared radiation characteristics are stable and obvious.The infrared radiation energy of the plume mainly ditributed at the infrared wavelength of 2.7μm and 4.5μm,which is in accordance with the actual situation.