The fiber end with polished inclined-surface is important to reduce the ASE and restrain the selfoscillations for the high power fiber amplifier. Physical models of fiber end with different signal input,output and coupling of pump light are set up. Theoretical analysis,numerical simulation of coupling efficiency and return loss of the fiber end with variable angles of the inclined surface are performed. The results show that the coupling efficiency and return loss of the signal light are affected obviously by the fiber inclined angle,which can improve the performance of the fiber amplifier if the angle is choosen properly.