In this Letter, a high-power Er/Yb-codoped fiber amplifier (EYDFA) with a high-reflection Yb-band fiber Bragg grating (FBG) at the pump end is experimentally investigated. The FBG was inscribed on a piece of double-clad fiber with a center wavelength of 1032 nm. Due to the selective reflection of the backward Yb-band amplified spontaneous emission (Yb ASE) by the FBG, a co-pump-propagating Yb-band auxiliary signal was generated. Because of the stimulated amplification and reabsorption of the auxiliary signal, the Yb ASE was dramatically suppressed and the pump conversion efficiency (PCE) of the EYDFA was notably improved. An output power of 6.48 W was achieved at a pump power of 16.5 W, which is equivalent to a PCE of ∼39%. The slope efficiency relative to applied pump power was ∼40%. The maximum output power was improved ∼20% because of the introduction of the FBG.