Global Navigation Satellite System-Reflectometry Synthetic Aperture Radar (GNSS-R SAR) is an integrated space-air-ground bi/multi-static SAR system comprising navigation satellites and low-orbit satellites or airborne/ground-based receivers, which can make full use of the existing navigation satellite resources, and has the advantages of a large number of satellites, flexible and diversified geometrical configurations, strong concealment, short revisit cycle, long observation time, etc. It is one of the important directions for the future development of air-ground and space-ground SAR radar networks.