Abstract: The operation principal of Er3+,Tm3+ co-doped silica fiber amplifier is presented when pumped at 980nm.Depending on the principal,the mathematical model of energy transfer process between Er3+ and Tm3+ ions is established.Based on the rate and propagation equations,numerical simulation of its steady state operation properties is performed and the simulation of output power spectrum of several channel signals as a function of different factors,(such as different fiber length,different pump power,and different Tm3+ ions concentration) is also given.The simulation results show that the amplifying bandwidth of this fiber is up to 90nm(twice larger than the traditional Er-doped fiber amplifier) and the average gain is up to 10dB when the pump power is just 400mW.Its characteristic of ultra-wide band amplifying is useful for DWDM in the near future.