In this paper, sound absorption characteristics of brick/block absorbing walls are investigated by the numerical analysis.A calculation method combining the wave scattering theory with the finite element method is introduced in order to make analysis on the sound absorption characteristics of brick/block walls with arbitrary neck shapes.The method is applied to hypothetical two dimensional brick/block absorbing walls, and it is found that the open-pipe resonance in a neck part and the standing wave in a backing space affect the sound absorption of the wall significantly at high frequencies.In addition, the method of controlling the sound absorption effect by changing the shape of the neck is investigated.The effect of changing the shape of the neck is confirmed by a 1/10 scale model experiment.