Abstract: A mathematic model of the micromechanism of porosity flaws in the adhesive layer had been built up. The characteristics of the lowest model SH waves propagating on the “sandwich” structure had been given by analyzing the dispersion equations of SH waves propagating on the structure. The results indicated that the thickness and efficiency modulus of the adhesive layer with porosity flaw could be expressed by the dispersion curves, a new nondestructive way to detecting the porosity flaw in the adhesive layer was presented.