Abstract: Actively mode-locked fiber lasers based on the semiconductor optical amplifier(SOA),which are capable of generating ultra-short pulse train with high quality and high repetition rates,have received considerable attention.After considering the facet reflectively of the SOA,a theoretical model of the harmonic mode-locked fiber ring laser based on SOA is established.Based on this model,the influence of the facet residual reflectivity on the shape,peak power,and pulse width of the pulse output from the harmonic mode-locked fiber ring laser is studied.The results show the residual facet reflectivity of the SOA affects seriously the shape of the mode-locked pulse.With the increase of the facet reflectively of the SOA,the peak power of the mode-locked pulse will be increased and the mode-locked pulse will be broaden.