Abstract: In order to acquire high power, single-frequency, single-polarization narrow-linewidth laser beam, a single-frequency erbium doped loop fiber laser and its amplification configuration were studied. With an un-pumped erbium-doped fiber as saturable absorber, with a high-reflectivity fiber Bragg grating as wavelength selector, a super narrow band filter was constructed. Fiber polarization controller and polarization-maintaining optical circulator with high extinction ratio were incorporated in the loop cavity to obtain single polarization output. A single stage amplifier was used outside the loop cavity to increase the output power. 206mW output laser was obtained, and the power stability reached 1.4%. The linewidth of output laser was less than 500Hz measured through fiber delayed self-heterodyne method. The degree of polarization was stable at 99.7%. The result shows that un-polarization-maintaining saturable absorber with fiber Bragg grating together with partially polarization-maintaining structure can lead to single-polarization narrow-linewidth laser,and laser amplification will broaden the linewidth.