Abstract: Based on rate and propagation equations,the output signal power and noise characteristics of double cladding erbium-ytterbium co-doped fiber amplifiers with a reflection are analyzed numerically. Due to the contributions of the reflector to reflect the un-absorbed pump power,pump light transmitted in the active fiber is increased and the output performances are improved.It is shown that the amplifiers with the reflector only using half-lengths of fiber have about the same high power output signal as those without reflectors,for forward pumping and backward pumping,noise figures are obtained less than 4dB.