The two-dimensional model of sound absorption layer containing period cylindrical holes indicates that: when the plane wave normally incidents, the acoustic performance of sound absorption layer has been controlled by the first axisymmetric wave, under the frequency where the propagating attenuation of the first mode is lower than that of other higher modes. Based on this conclusion, the effective impedance of cylindrical tube, which represents the unit cell of sound absorption layer, has been derived. Besides, together with the transfer matrix method, the simplified model for the acoustic performance prediction of sound absorption has been obtained. Next, the genetic algorithm has been used to simultaneously optimize material properties and structural parameters of sound absorption layer which contains periodical cylindrical-conical holes, and the conclusion indicates that compared to the single optimization of material properties, the simultaneous optimization of material properties and structural parameters may result the higher sound absorption coefficient in a wider frequency range.