Based on the discrete particle model，which is used to solve the solid phase and to obtain the individual grain¢s information such as location，velocities and displacements，etc.，Darcy seepage model for the analysis of fluid-solid interaction in granular materials with interstitial water is proposed. Combined with the characteristic based smoothed particle hydrodynamics(SPH) method that is used to get Darcy¢s velocities，the numerical solution scheme for the seepage model of saturated and unsaturated granular materials is presented. Numerical results demonstrate the capability and good performance of the proposed model in modelling the fluid-solid interaction and deformation in granular materials with interstitial water.