Abstract: To design proper algorithms for ultra-wide field of view (FOV) infrared fisheye warning system, the infrared image taken by the ultra-wide FOV warning system was studied. The target in the infrared image is a point target, and its background is complicated. For the sky background, its radiance will decreases and target moving track will be bent as the elevation angle increases. Such situation is deteriorated with the increase of FOV angle. Based on the design theory of the infrared fisheye lens, the illumination of the system image plane was analyzed and calibrated with CDS100-04 black body. It is found that the relative standard deviation of the gray value in different positions is only 2.26%, which indicates good image illumination uniformity. Finally, the detection distance of this system is analyzed, which is about 9.6km.