Based on analysis of background radiations characteristic in space and the different reflection characteristic of diffuse target to the coherent light and natural light, through using statistical signal detection theory, the formula of working distance of space-borne charge coupled device (CCD) gaze imaging tracking system under laser illuminating active tracking mode and sun illuminating passive tracking mode are studied, respectively. The result indicates that the space-borne CCD gaze imaging tracking system can track 1 m2 diffuse target in 10 km distance under 1 mJ pulse energy laser active tracking mode, and the working distance of sunlight passive tracking mode is as high as hundreds kilometers.