Abstract: Reverberation caused by rough surface scattering is investigated using the coupled mode theory.Firstly, coupled coefficients that describe the scattering caused by irregular bottom or rough sea surface are derived based on coupled mode theory.Then the decaying rules of surface reverberation level are simulated in different sea states, which are realized according to Pierson spectrum,and the surface effect on the bottom reverberation is also discussed. The emphasis of this paper is to demonstrate the mechanism of rough surface scattering by describing the transfer of energy between different modes.It is indicated that bottom reverberation,which is dominated among other kinds of reverberation in shallow water,is effected by the sea surface scattering as the sea state level increases.