This study realizes a fiber laser based on a ring cavity, directly pumped by a 793 nm laser diode (LD) and operating in the 2 μm waveband with tunable wavelength and narrow linewidth. A tunable fiberized Fabry-Perot (F-P) filter is inserted into the ring cavity to obtain wide wavelength tuning. By using an unpumped polarization-maintaining thulium-doped fiber as a saturable absorber, a dynamic narrowband grating is generated in the cavity to achieve narrow linewidth laser output. After optimizing the lengths of gain fiber and saturable absorber fiber, the obtained output power of the laser reaches up to 70 mW and the wavelength tuning range is as high as 98 nm, and the tuning range is 1950-2048 nm. The average spectral linewidth of the narrow linewidth laser is 0.86 GHz in the wavelength tuning range. This laser can serve as a seed source for fiber amplication to obtain a high-power 2 μm laser with narrow linewidth and wide tunable wavelength.