Abstract: In this paper,a new theory about sound absorption by pseudostochastic diffusors is proposed.A quantity. "coupling specific acoustic impedance" is introduced,which represents coupling between adjacent wells of the structure.The variation of particle velocity and sound pressure in the vicinity of the opening of wells is investigated and the exact solution of the lst approach is derived.Moreover,the nonlinear effect is discussed.The rigorous formula to calculate the nonlinear coupling specific acoustic impedance is derived.Typical calculation shows the nonlinear effect can apparently improve the sound absorption character of the structure even if the sound pressure level of incident wane is medial.