Abstract: This paper reviews the research and development of geosynchronous synthetic aperture radar (GEO SAR) technology in recent years. Firstly, it introduces the typical GEO SAR systems proposed domestically and internationally under different technical routes, analyzes the orbit selection, system characteristics and main application of these systems and summarizes the research progress in large-scene imaging and moving target imaging algorithms for GEO SAR. Then, it describes the four key techniques that need to be broken through in GEO SAR systems, GEO SAR mission design, high-power transmitter technique, large deployable reflector antenna design and SAR imaging with long integration time. In terms of GEO SAR applications, the paper compares the advantages of GEO SAR over low-earth orbit SAR (LEO SAR) and analyzes the application prospects of GEO SAR in fields ranging from disaster prevention and rapid emergency response, marine target monitoring, to natural resource surveys. Finally, by summarizing and analyzing the existing technologies, the paper outlines the future development trends of GEO SAR technology.