An example，the optimization of electromagnetic parameters for a special-structured electromagnetic wave absorber are computed by using multi-objective functions. Some parameters with absorptivities>20db with in 5～15GHz and the absorption curves of perpendicular and parallel polarization at incident angle 0°,20°, 45°and 60°corresponding to these parameters are given.It is proved that good absorption characteristics can be obtained even if some inserted layers' do not absorb，provided that the parameters for all layers are optimized. It is difficult to obtain high absorptivity by purely using electronic or magnetic absorber. “Gradual impedance transition” is not the only method to get good electronic matching. For a transmission material with emergent side being “free space”，a good impedance matching can be obtained only at ε_r≈μ_r when using materials do not possess absorbency.