Abstract: The governing equations for dynamic analysis of saturated porous medium, which are obtained by the general framework of averaging theories, are described in the paper. A generalized plastic constitutive model for fully saturated soils is adopted in the computational process. Samples of medium loose and dense sands are studied. Negative water pressures, which are important for localization phenomena in the shear band of fully saturated dilatant geomaterials, are obtained for dense sands, while positive water pressures are obtained for medium loose sands. All the results obtained by numerical simulation are consistent with the phenomena observed in laboratory test.