A fast reflective scanning imaging system is constructed by employing the terahertz (THz) quantum-cascade laser as the light source and the low-temperature bolometer as the signal receiver. A rotational and translational platform is used in this imaging system to realize fast scanning. The fast imaging process of a circle area with a diameter of 80 mm is demonstrated by a computer controlling the scanning platform to carry out the rotational and translational motion. The signal intensity and the related 2D sample position are acquired simultaneously. By the imaging system, the scanning time is 5 s and the spatial resolution of the obtained image is 1 mm, which greatly shortens the imaging time. Furthermore, the optical components are reduced effectively by the co-optical path design based on THz beam splitters, which reduces the size of the THz imaging system.