High-power narrow linewidth (HPNL) linearly polarized all-fiberized lasers have been widely used in industrial, medical, scientific research, and national security fields. Enhancing the brightness of such fiber lasers has always been a focus of researchers. Firstly, the physical factors that limit the power increase and beam quality maintenance of HPNL fiber amplifiers are analyzed, and corresponding mitigation measures are discussed. Then, the research progress of HPNL linearly polarized fiber lasers is reviewed, and some representative achievements are introduced in detail. Finally, the future development trends are discussed and outlooked.