Abstract: Owing to the fact that no existing theoretical formula can be used to calculate the absorption coefficient of the multi-layer absorbers composed of perforated plates,cavities and porous absorbers,a theoretical method for this calculation is proposed in this paper.First,the acoustic impedance and the absorption coefficient of the multi-layer absorbers composed of perforated plates and cavities or perforated plates and porous absorbers are calculated by using the sound-electro analogy.Then,the acoustic impedance and the absorption coefficient of the multi-layer absorbers composed of perforated plates,cavities and porous absorbers are calculated by using stepped deductions.Theoretical calculation of the absorption coefficients of three types of multi-layer absorbers composed of different materials including perforated plates is carried out,and the results indicate that using this method to calculate the absorption coefficients of the multi-layer absorbers is feasible in contrast with the experimental results.