An optically pumped gas terahertz fiber laser based on gold-coated quartz hollow-core fiber is demonstrated. When the terahertz fiber laser is filled with methanol gas and pumped by a piezoelectric-ceramic-transducer-adjusted transversely excited atmospheric pressure carbon dioxide laser, a continuous 2.52 THz laser with the output power of 110 mW is obtained. Attributed to the adjustment of the piezoelectric ceramic transducer in the carbon dioxide laser, the fluctuation of the terahertz fiber laser output power is controlled within ±5%. The result confirms the possibility of a compact flexible optically pumped gas terahertz fiber laser.