The invention is applicable to the technical field of security check and provides a terahertz imaging system and a terahertz security device. The terahertz imaging system comprises a terahertz radiation module, an optical chopper, an imaging objective lens, a light-sensitive surface, a terahertz detection module and a signal processing module; the optical chopper is used for modulating terahertz wave radiated by the terahertz radiation module into terahertz wave with default frequency and radiating the terahertz wave to a to-be-detected object in a covering manner; the imaging objective lens is used for focusing the terahertz wave carried with complex dielectric function information of the to-be-detected object on a focal plane of an image space; the minimal edge length of the light-sensitive surface is greater than or equal to the maximum edge length of an imaging region of the imaging objective lens, and the terahertz detection module is used for converting the terahertz wave carried with the complex dielectric function information into an analog current signal; the signal processing module is connected with the terahertz detection module. By the arrangement, nondestructive detection can be performed on human body or biological tissue, radiation injury can be reduced, complete detection data of the to-be-detected object can be acquired by one radiation, detection efficiency is improved, and high-risk items of metal, poison, explosive and the like can be effectively identified.