Aiming at low-loss terahertz (THz) fiber fabrication, we propose a negative curvature terahertz tube fiber (NC-TF). Simulation results show that the NC-TF has similar transmission losses (TLs) to the recognized half-ring fiber but with a significantly simpler fabrication structure. NC-TF samples are fabricated by extruding polymers from a specially designed mold, presenting a novel approach for obtaining fibers with shaped boundaries. Experimental data demonstrate that the NC-TF exhibits TLs below 3 dB/m in transmission bands, with a minimum TL of 0.2 dB/m at 0.6 THz. The simplicity and practicality of the NC-TF enable its application in various THz transmission or sensing scenarios.