Abstract: Terahertz technology has been developed rapidly over the past few decades. As a powerful tool for charactering biomacromolecules, terahertz spectroscopy and imaging technologies have been demonstrated their broad prospects in diagnostic and clinical medicine. The specific components of biological samples can be quantitatively analyzed by a terahertz spectroscopy, and similarly, the spatial distribution of the components measured in samples can be detected with terahertz imaging systems. This paper reviews some representative in the fields of terahertz diagnostic medicine based on the types of terahertz optical systems, some investigations on terahertz biological effects are introduced from the level of biological individuals, tissues, cells, and biological macromolecules. Although this field is still in the trial and preliminary exploration stage, there are many pioneering researches with great potential have been proposed, such as terahertz-assisted targeted drug transmembrane transport and terahertz cancer cell DNA demethylation. Finally, the research status of terahertz biological effects is summarized and the key directions and possible breakthroughs in this field are analyzed and prospected.