In infrared remote target detection system,the sky-background changes slowly,but the target shows the partial corner. It has a broad gray range and is brighter than the background. According to these characteristics,a target segmentation algorithm based on partial histogram is presented. The distribution characteristics of multi-target histogram are analyzed. According to gray level distribution rule and the image pixels restriction,the image segmentation is realized. Experiment results show that this method can segment flying targets rapidly and effectively,and it has strong practicability.