Terahertz radiation is an electromagnetic wave whose frequency is in the range of 0.1 THz～10 THz. With its many features such as non-ionizing and resonance to many biomolecules, THz wave has great potential applications in biomedical field, especially in tumor detection. Terahertz imaging technology, as a new imaging technology in biomedical field, is studied by many research groups around the world. In this paper, we listed and analyzed many terahertz imaging methods in tumor detection, including terahertz scanning imaging, terahertz tomography, terahertz holography, and terahertz near-field imaging. We introduced the basic principle of these imaging methods and the works done by different groups worldwide. At last, we presented the prospect of terahertz imaging technology applied in biomedical field.