Narrow linewidth fiber lasers have gained extensive attention as their important applications in geoscience, nonlinear frequency conversion, and beam combining. Unfortunately, the output power of narrow linewidth fiber lasers is limited by nonlinear effects such as stimulated Brillouin scattering (SBS), self-phase modulation (SPM), and four wave mixing (FWM). Lots of methods have been proposed to suppress the nonlinear effects, which boost the output power of narrow linewidth fiber lasers up to kW level. In this paper, we give an overview of the research on high power narrow linewidth fiber lasers at the wavelength of 1 μm. The nonlinear effects and corresponding suppressing methods are introduced, as well as the recent progress and key factors of high power narrow linewidth fiber lasers.