A terahertz metamaterial waveguide (meta-waveguide) and a meta-waveguide-based lens-free imaging system are presented. The meta-waveguide not only inherits the low-loss transmission performance of a waveguide but also breaks through the diffraction limit under the action of the metamaterial, achieving subwavelength focusing. The focusing distance is far greater than the Rayleigh length, thus enabling far-field scanning imaging. For verification, a metal ring-based meta-waveguide was fabricated by 3D printing and metal cladding technology. Then, a transmission scanning imaging system working at 0.1 THz was built. High quality terahertz images with a resolution of 1/3 of the wavelength were obtained by placing the imaging targets at the focus and performing two-dimensional scanning. The focusing and transmission of terahertz wave in the meta-waveguide were simulated and analyzed.