In order to investigate the impact of the amplified spontaneous emission (ASE) on the performance of high-power pulsed Er-Yb codoped fiber amplifiers (EYDFAs), several EYDFAs with different input signal parameters are studied numerically. The results show that the Yb-band (1.0~1.1 μm) ASE is the main factor that limits the efficiency of a high-power pumped EYDFA. Therefore, suppressing the Yb-band ASE can effectively help to improve the performance of the amplifiers. It is found that adding an Yb-band signal at the pump end can help to reduce the Yb-band ASE effectively. Simultaneously, this method can also enhance the power conversion efficiency and improve the output power of the amplifiers.