Terahertz(THz) lies between far-infrared and microwave in electromagnetic spectrum with frequency form 0.1 to 10 THz. Terahertz is believed to be the master technology of international electronics and information science, and to be the bridge between micro-electronics and macro wavelength. THz contains great prospect in the electronic, information, life, national defense, aerospace, etc, and has formed a worldwide research climax. This article introduces the main character，primary researchs and applications of Terahertz.