By analyzing the basic imaging principle of detecting the concealed objects beneath clothes,the advantages of passive millimeter wave and terahertz imaging for human body screening and the best operation frequency and temperature of the imaging system are discussed.Through an aspect of discussing the key technologies that impact on the image quality,the development of passive millimeter wave and terahertz imaging are introduced.The key technologies include quasi-optical imaging principle and mechanical scanning method,Schottky diode detector and superconductor detector that are commonly used in passive millimeter wave and terahertz imaging,and the digital image processing and object auto-detection method of passive millimeter wave and terahertz image are also introduced.Finally,a personal opinion is put forward on the application prospect and future development direction of passive millimeter wave and terahertz imaging in security check.