Abstract: Satellite-to-satellite tracking is a new technique to resolve the series of problems met in the determination of the earth's gravity field. As the key technique of SST-ll, KBR can get SST-ll measurements directly. So the KBR performance analysis is the first step in SST-ll design. Assuming that the satellite pairs of SST-ll are in near circle polar orbits, the spectrum relationship between the earth gravity field and KBR is established using an analytic method. Then some examples are analyzed, the suggestions and conclusions are drawn from these examples. The research results can be a reference for future satellite gravity project of China.