Stimulated Brillouin scattering has attracted a lot of attention for its interesting characteristics which are very promising for applications including Brillouin fiber lasers, optical amplifiers, and distributed fiber sensors. Its linewidth narrowing effect make it possible to generate Brillouin fiber lasers with narrow linewidth, although many results are restricted in some ways such that the excellent performances on output linewidth, output power and insensitivity to environ- mental perturbations can not be all achieved. In this thesis, we demonstrate a polarization-maintaining Brillouin fiber laser with the short-term linewidth less than 2.5 kHz and the output power as high as 100 mW when the pump power is 700 mW. The linewidth ratio between the pump laser and the Stokes light is enhanced to be 800 times, much better than the conventional results of 50 times.