The invention discloses a THz Raman fiber laser consisting of a pumping source, a coupled system and a metal plating gaseous core fiber; the core of the metal plating fiber is filled with THz active gas, the front and back ends of the fiber are additionally provided with sealing caps, and the heads of the sealing caps are parallel with that of a metal plating hollow fiber. The pumping source is an RF-operation CO2 or N2O laser and the coupled system is an infrared laser lens combination coupled system. With the core filled with low pressure THz active gas, the low-loss metal plating fiber of the Raman fiber laser is made into a THz active fiber to replace a bulky silica tube or big vessel. As an infrared laser pumping fiber is used for producing THz wave, the active trail of pump light isconsiderably increased in the fiber. Compared with the silica tube or big vessel, the efficiency of the fiber with the same length is higher. And due to the light weight, small volume and flexible property of the fiber, the whole set of instrument is compacter and nimbler.