A high-power all-fiber single-frequency polarization-maintained (PM) laser operating at 1 083 nm is demonstrated using a master oscillator power amplifier (MOPA) structure. The seed source of this MOPA laser system is an in-house-built ring-cavity fiber oscillator. Four-stage amplification configuration is employed, in which the maximal output power of the main amplifier is 90.4 W, corresponding to a conversion efficiency of 72.5%. The polarization extinction ratio of the output light is 13 dB. The amplified spontaneous emission is suppressed by a factor of over 25 dB, and no stimulated Brillouin scattering effect is observed when a large-mode-area and high absorption coefficient PM gain fiber is employed.