A cladding-pumped single-mode ErYb-codoped fiber amplifier which is seeded by two lasers at 1535 nm and 1064 nm is designed to suppress the harmful Yb emission. An inband core-pumped fiber amplifier is constructed with the 1535 nm laser. The output power and spectrum of the amplifier are measured with different launched pump power. A 1.22 W maximum output power with 58.4% slope efficiency is achieved when the gain fiber is 5 m long, the seed laser power is 80 mW, and the 1535 nm pump power is 2.1 W. The output power and efficiency of a traditional amplifier whose pump source is 976 nm laser diode are also measured. The experimental results indicate that inband-pumped fiber amplifier can achieve higher efficiency than traditional fiber amplifiers.