In this letter, millimeter wave attenuation by flat sea surface covered by foam is reported. This was achieved by developing an analytical model of foam-covered sea surface using the finite difference method (FDM) method, which is a solution to the Parabolic Wave Equation (PWE) method. The PWE has been widely used to solving Electromagnetic (EM) wave extinction and radio wave propagation in random media problems. The FDM method investigates attenuation of EM waves propagating through slices of sea foam layer as functions of frequency, foam layer thickness, polarization and angle of incidence. Results obtainedshowed that attenuation increases with the depth of sea foam layers and decreases with increase in propagation angle for various WindSat frequencies.