Abstract: A hollow-core porous microstructured terahertz fiber based on Topas cyclic-olefin polymer (COC) was designed and manufactured. The loss characteristics of an optical fiber with outer diameter 10 mm was simulated using comsol software in the 0.2-1.5 THz band. There are several low-loss bands in the 0.85-1.5 THz, and there are three windows in which the loss is lower than 3 dB/m in the 0.85-1.1 THz band, the loss is about 0.208 dB/m especially in the 0.99 THz. By comparing the loss characteristics of the fiber with core diameter of 3 mm, 4.8 mm and 6 mm in 0.8-1.5 THz band, the loss was reduced with increasing the diameter. The outer diameter of designed THz fiber was enlarged to 7 cm, and a dedicated mold was designed for manufacturing preform. A 22 cm long THz fiber preform with a standard structure and smooth surface was manufactured by the hot extrusion molding method. Finally,through the laboratory's unique draw tower, the terahertz fiber of the core diameter of 3 mm, 4.8 mm and 6 mm were manufactured. The loss analysis result show that the average loss of the fiber with core diameter of 6mm is 2.175 dB/m in 1.27 THz and it is near the theoretical loss (1.95 dB/m).