Based on terahertz time-domain spectrscopy (THz-TDS) technology, a broad-band time domain terahertz radar system can be used to do research on scattering characteristics of objects. At present, the optical structure and mechanism of this system-showing the radar detection principle and imaging mechanism-has attracted a lot of interest in the terahertz research field. Based on the femtosecond Ti: sapphire osillators pumped terahertz time-domain spectrscopy system, this paper constructs the first terahertz radar system in this country (0.11.3 THz). System calibration is carried out by measurements on standard metallic spheres. Three military scale models are measured by the Radar system. The shapes of the models are retrieved by the improved back projection algorithm, which verifies the new imaging mechanism based on time domain scattering signal. With high frequency broad band spectrum and high imaging resolution, the terahertz radar would make great contribution to stealth military units design and become a new research platform on terahertz scattering characteristics.