The self-phase modulation (SPM) and spatial hole burning (SHB) at low power can lead to the output spectral broadening of a fiber laser.The effects of the bandwidth and reflectivity of OC (output coupler fiber Bragg grating) on fiber laser output spectral broadening were analyzed.The laser output spectral width changes with the bandwidth and reflectivity of the OC under different output powers were experimentally investigated.Experimental results show that the decrease of OC bandwidth can effectively reduce the output spectral broadening caused by SPM and SHB.The decrease of OC reflectivity can reduce the SPM-induced output spectral broadening speed and promote the SHB-induced spectral broadening.But in the same amount of change,the influence of bandwidth is more significant than that of reflectivity.The experimental results are consistent with the theoretical analysis,which has a great significance for the design and application of spectral beam combining and narrow linewidth high power fiber lasers.