Abstract: In this paper, the problem of evolution of slowly modulated wave train on porous sea bed is investigated with the method of multiple scales. For the sea water in the upper region, the classical potential theory is used while the fluid motion in the porous sea bed is described by Darcy’s law. The equations of the first and second order modulations of wave amplitude are derived by using matching conditions on the sea bed. The corresponding solutions are found and seepage pressures are also given at the same time.