Terahertz (THz) radiation is a newly developed coherent far infrared source, which has been applied in many research fields, especially medical application and biological application. In the present paper, the mechanism and methods of its generation and detection are introduced. The properties and its uniqueness in applications to biological researches and DNA molecular spectroscopy are discussed. A brief review is given to the latest progress in THz spectroscopy of DNA samples, and the prospect of the research in this cross-discipline is presented.