Abstract: When waves propagate over a porous sea bed,the strength of soils in seabed will vary non-uniformly with depth.On the basis of Biot’s consolidation theory,the distributions of the volume strain of soils along the depth was discussed considering of influences of permeability,shear modulus,wave period,water depth and soil thickness.It was shown that under the action of waves,there’s a hard layer at the depth of 0.12 wavelength in silty seabed of infinite thickness;the wave-induced hard layer was at the surface of seabed when the thickness of sediment was less than half a wavelength;when the thickness was larger than half a wavelength,the wave-induced hard layer was at a depth increasing as seabed thickness increases;the wave-induced strength of soils was apparently non-uniform under the influence of shear modulus and permeability of soil,wave period and water depth.