To optimize the fiber amplifier,an Yb/Er co-doped double cladding fiber amplifier pumped at 980 nm was analyzed numerically.The gain of the amplifier with different signal powers was analyzed and the distribution of population inversion,pump power and signal power along the axis direction of the fiber were calculated at stable state.According to the numerical results,a fiber amplifier with 10 m Yb/Er co-doped double cladding and launched maximum pump power of 6 W was set up.Proposed amplifier shows the maximum output power of 1.9 W and slope efficiency of 23.4% on conditions of the initial signal power of 0.5 W.