With the configuration of double-grating and two-stage amplifying, the optical fiber amplifier realizes high gain-clamped and high output power, controlled by two controlling lasers of different wavelengths. As input power ranging from -5.1 dBm to 2 dBm with the power attenuations of optical attenuators as 33.2 dB and 3.8 dB, the maximum output power comes to 1.55 W, while the average gain and noise figure of the gain-clamped fiber amplifier are approximately 30.3 dB and 6.4 dB, respectively. Furthermore, the gain′s excursion is limited in 0.27 dB. The range of clamped gain can be 24.5 dB~31.3 dB, while the gain′s excursion is less than 0.3 dB. As the powers of remaining channels are 0.74 mW and 1.57 mW respectively, the ranges of excursions are less than 0.08 dB and 0.16 dB with double channels existing in the gain-clamped amplifier.