In order to improve the THz imaging speed, an image surface scanning THz fast imaging system was designed. It was a single pixel imaging system basing on the reflection type. The system collected THz by an off axis parabolic mirror which was used to realize the imaging of large caliber, high transmittance, high quality imaging. The optical parameters of system were that F/# was 2.93, the aperture diameter was 120 mm, the field angle was ±1°, the focus length was 293.45 mm, the size of imaging window was 64 mm×64 mm, the diameter of circular hole was 2 mm, the imaging speed of 16×16 pixels was 0.1 min, the imaging speed of 32×32 pixels was 0.47 min, the imaging speed of 64×64 pixls was 1.7 min, and the spatial resolution was 10 mm. The system combined with compressed sensing theory and image surface scanning theory realized the fast imaging property. A rotation plate with holes was inserted at image surface position, which scanned the THz intensity. Then a light cone was employed to collect energy to the Golay detector. The device output image by a special situation of compressed sensing theory that the sample number equaled to the image pixels. Sequentially, the regular least squares algorithm was used to reconstruct intensity distribution. The system has the property of high imaging speed and resolution, low costs, and small structure.