We report a continuous-wave high-output power and narrow-linewidth all-fiber laser at 1550 nm with the master oscillator power amplifier (MOPA) configuration. An all-fiber distributed feedback seed laser was boosted by three cascaded fiber amplifiers. In the experiment, we adopted a large-mode-area (LMA) Er3+:Yb3+-co-doped polarization-maintaining fiber to increase nonlinear thresholds and avoided the broadening of the laser linewidth. A linear-polarization fiber laser with average output power of 20 W, linewidth of 0.88 kHz, and power jitter less than 2% was finally achieved.