Abstract: An introduction to the state of the art of terahertz (THz) technology is presented.The characteristics of THz waves are described briefly, followed by a detailed review of THz radar systems. Terahertz radar is known to be superior in military applications due to its anti-stealth capability,high resolution, broad bandwidth, adaptability to the environment, low interception rate, and strong anti-interference and plasma penetration abilities. These advantages will lead to potential applications in national defense and security.