Polarization-maintaining-ytterbium-doped double-clad fiber of 20 μm diameter core and 400 μm diameter clad size (PM-YDF 20/400 μm) was fabricated using the modified chemical vapor deposition method and solution doping technology. The numerical aperture of the fiber core was 0.062, and the cladding absorption coefficient of the fiber at 976 nm was 1.4 dB/m, as measured using the truncation method. To examine the effectiveness of fiber laser performance, an all-fiber master oscillator power amplifier testing platform was used. The PM-YDF 20/400 μm has a length of 15.3 m, and its bending diameter is 10 cm. Furthermore, a narrow linewidth linearly-polarized laser output of up to 3.008 kW is achieved using a pump power of 4.143 kW at 976 nm. The full width at half maximum linewidth is 0.213 nm, corresponding to a slope efficiency of 75%. At a laser output power of 2.009 kW, the polarization extinction ratio is 16 dB and the beam quality factor is 1.19 and 1.20. Moreover, stimulated Brillouin and Raman effects are effectively suppressed.