Abstract: Space based early warning radar (SBEWR) break through the limitation of the earth’s curvature on the viewing range of ground-based and airborne radars, enabling top down observation of targets in the air, on the ground and on the sea surface. They can integrate multiple functions to achieve rapid perception and update of regional situations and are an important component of national defense. This paper surveys the domestic and international SBEWR. A review of the relevant literature and a comparative analysis of the three main SBEWRs show that the distributed SBEWR system has gradually become a current research hotspot. According to the characteristics of distributed SBEWR, the research progress of key technologies including the systematic design technologies, large scale deployable antennas and clutter suppression algorithms is investigated. Some suggestions of the future development of SBEWR for national defense are given.