The skin infrared (IR) characteristics of a Unmanned Aerial Vehicle (UAV) is the most important basis for the detection and recognition of the UAV. And the aerodynamic heating of an UAV′skin, the heat transfer by solar radiation and earth radiation are the key factors that are contribute to the skin IR characteristic of the UAV. The skin IR characteristics calculation model of an UAV was built based on the environment′ infrared radiation and that of the UAV in this work. The one-dimensional heat conduction difference equation of the UAV skin was found out by a forward-difference method. And then, based on which, the IR radiation intensity distribution of the UAV in a certain plane was calculated by importing the skin emissivity of an UAV. Finally, it is concluded that the IR radiation intensity of an UAV at 8-14 μm band is far greater than that at 3-5 μm band. And at the same band, the radiation intensity of the top skin is higher than that of the bottom skin.