The terahertz imaging radar is suitable for near field detection because of the advantages of short synthetic aperture time and high resolution. Nevertheless, due to the limitation of device maturity, large distortion of the radar system reduces the signal quality. At the same time, system inherent delay causes the deviation of target range. All of these problems will degrade the imaging quality. In order to solve these problems, the amplitude and phase error compensation method which is estimated by the least square method, and the inherent delay correction method are put forward, and the measurement method of the system distortion is given. The test results show that after compensation, the resolution of image is improved and the quality of imaging is enhanced effectively.