Design of the waveguide amplifier nonuniformly doped with Er along the propagating direction is presented. The model of waveguide amplifier is constructed by using the finite element method, including cooperative upconversion, cross rela xation and excited state absorption. The gain performances at a given length and at maximum are improved to be 1027% and 565%, respectively. Calculation res ults agree qualitatively with the experimental data of cascaded Er_doped glass s amples.