A flexible tube-lattice fiber is introduced into a THz-TDS system to implement a THz false-color imaging system. The fiber, which has three low-loss transmission windows in the frequency range of 0.1–1 THz, can lead THz radiation out of the system and lead back to the detector. It can be used as a probe to break the spatial limit of the THz-TDS system and widen the range of applications. A cuvette filled with two different kinds of white powder was used as a sample in the experiment. One end of the fiber was fixed and the other end near the sample was scanned by a 2D translation stage across the sample. THz radiation from the fiber passes through the sample and is reflected by amirror at the back of the cuvette. The reflected THz radiation contains the sample’s THz spectral information. Thus, the entire sample can be investigated by scanning the fiber. Three-primary colors (red, green and blue) are defined by spectral intensities of the fiber transmission windows. A 13 × 16 pixels false-color image was generated with the mix of values of the primary colors. In the false-color image,the two kinds of powder, the cuvette and the background present different colors and saturation which indicate different materials and the concentration, respectively. The resolution was also investigated by scanning slits in a metal sheet. The resolution of the imaging system is approximately 1 mm.