The invention discloses a mail detection device and method. Specifically, the device includes: a broadband terahertz generator, a collimator, a beam splitter, a fixed reflector, a mobile reflector, a wave buncher, a flat-panel detector, an acquisition card and an information processing module. Specifically, the information processing module is used for generating a terahertz image of a to-be-detected mail according to an electric signal sent by the acquisition card when the mobile reflector is motionless; and when a suspicious object is found according to the terahertz image of the to-be-detected mail, the information processing module controls the mobile reflector in terms of displacement, and generates the spectral information of the suspicious object according to the electric signal sequence sent by the acquisition card in the displacement process of the mobile reflector.