Abstract: The passive radar based on external illuminator has many advantages,such as good invisibility,anti-stealth,anti-jamming capability,and it is simple and reliable.The factor to affect the performance of the passive radar is as following:direct-path-wave,multi-path effect,co-channel interference,etc.,and in the process of designing the passive radar system,these factors must be mainly considered.Recently,the passive radar has attracted more and more attention,so the technology of passive radar has developed rapidly.In this paper,firstly,the principle and composition of the passive radar are introduced,and then the key technology of the passive radar is discussed and analyzed.