Abstract: Assuming that the rough surface is a stationary process with a normal distribution, the scattering of a plane acoustic wave by this surface is studied. The statistical mean of the reflection coefficient and its relation to the correlation radius of the random surface have been discussed. By introducing the concept of the "equivalent reflecting plane", a general formula for a field with a point source in a stratified medium which has a random surface is derived. This demonstrates an easy solution to the additional attenuation coefficient under various sea conditions. The additional attenuation coefficients of the normal modes in the surface duct are given in detail.