The characterization of the multi-channel gain spectrum for erbium-doped tellurite-based fiber amplifier(EDTFA) in WDM system is presented theoretically. The numerical simulation results show that the effect of erbium-doped concentration on each channel signal gain is different when the pumping configuration, pumping power and fiber length are given. With the increasing erbium-doped concentration in tellurite-bascd fiber, the signal gain of shorter wavelength channels easily tends to saturate and attenuates quickly compared to that of the longer wavelength channels, also the multi-channel signal gain spectrum shrinks to L band.