Abstract: An all-fiber 1064 mm linearly polarized single-frequency fiber laser based on the master oscillator-power amplifier structure is reported. The seed was a single-frequency fiber laser with a line width of about 3 kHz. The seed laser with an output power of 50 mW was amplified by two-stage Yb-doped polarization-maintaining double-cladding (the core diameters are 10 μm and 20 μm respectively) fiber and a stage chirally coupled core gain fiber, and the high power single frequency fiber laser output with an output power of 138 W, the beam quality M²≤1.1 and the polarization extinction ratio better than 18 dB was finally obtained. At the pulse modulation mode, a linearly-polarized single-frequency fiber laser output with a peak power of 465 W and a pulse duration of about 500 μs was obtained.