Based on the self-developed large mode area Yb-doped double-cladding 25/400 μm active fiber with uniform doping and low thermo-optic coefficient, an all-fiber high-power narrow-linewidth fiber laser amplification experiment was carried out. The laser system achieves a single-mode fiber laser output with a maximum power of 2.2 kW, a linewidth of 25 GHz, and a center wavelength of 1060.3 nm, with a slope efficiency of 78% and a beam quality factor of M2≈1.2. This is the highest output power currently reported for narrow-linewidth single-mode amplifiers based on domestic Yb-doped double-cladding 25/400 μm active fiber, to the best of our knowledge.