Optical fiber fuse effect is the main cause of optical fiber laser path damage，and also an important bottleneck factor limiting the output power improvement of optical fiber laser. The optical fiber fuse damage effect in narrow line-width lasers at 1 560 nm band is studied in this paper. The conditions and causes of optical fiber fuse effect from the perspective of the mechanism of optical fiber fuse effect are analyzed. And in the output power range of 4~9.9 W，for the single-mode polarization-maintaining fiber with a mode field diameter of 10.5 μm，the verification experiment is carried out to determine the power density threshold corresponding to the occurrence of fiber fuses 11.44 MW/cm². A comprehensive method of hardware current limiting and temperature early warning to optimize heat dissipation is proposed，which reduces the probability of fiber fuse damage，and is conducive to improving the long-term stability of narrow line-width lasers working at high power.