A novel anti-resonant fiber for low-loss terahertz waveguides is proposed and analyzed. The terahertz fiber uses high-resistivity silicon as the bulk material and nine nested double-layer concentric circular tubes in the cladding to reduce propagation losses. The effects of the geometric parameters on the propagation characteristics are analyzed by the finite element method. The result indicates that an ultra-low total loss of 4.9×10-4 d B/m is achieved at f=1T H z. The low-loss propagation window is 0.48 THz ranging from 0.6 to 1.4 THz. In addition, the influence of mechanical bending on the propagation loss is investigated and the bending loss can be maintained at less than 7.3×10-3 d B/m at f=1T H z even if the bending radius is larger than 60 cm. The properties of this anti-resonant fiber are significantly superior to those of previously reported structures and the fiber thus has large commercial potential.