Abstract: In this paper the Staring Infrared Imaging System process is divided into two stages, the one is related with the target distance, another with the sensor only. The apparent radiance of the surface target and the expression between the pixel gray and the apparent radiance were deduced based on each stage respectively. Then the aerial and ground surface target distance was deduced based on the single-station dual-band infrared image. Lastly the algorithm was validated by the IR images got from the aerodrome etc, and the results and ranging errors were analyzed.