—A joint probability density function(PDF)for surface slopes in two arbitrary directions is de-rived on the basis of Longuet-Higgins’s linear model for three-dimensional(3-D)random wave field.andthe correlation moments of surface slopes.as parameters in the PDF.are expressed in terms of directionalspectrum of ocean waves.So long as the directional spectrum model is given.these parameters are deter-mined.Since the directional spectrum models proposed so far are mostly parameterized by the wind speedand fetch.this allows for substituting these parameters with the wind speed and fetch.As an example.thewind speed and fetch are taken to be 14 m s and 200 km.and the Hasselmann and Donelan directionalspectra are.respectively.used to compute these parameters.Some novel results are obtained,One of the in-teresting results is that the variances of surface slope in downwind and cross-wind directions determined bythe Donelan directional spectra are close to those measured by Cox and Munk(1954).Some discussionsare m -A joint probability density function (PDF) for surface slopes in two arbitrary directions is de-rived on the basis of Longuet-Higgins’ linear model for three-dimensional (3-D) random wave field. And the correlation moments of surface slopes.as parameters in the PDF.are expressed in terms of directionalspectrum of ocean waves .So long as the directional spectrum model is given. these parameters are deter-mined.Since the directional spectrum models are so far are mostly parameterized by the wind speed and fetch.this allows for substituting these parameters with the wind speed and fetch.As a example. thewind speed and fetch are taken to be 14 ms and 200 km.and the Hasselmann and Donelan directionalspectra are.repectively.used to compute these parameters.Some novel results are obtained, One of the in-teresting results is that the variances of surface slope in downwind and cross-wind directions determined by the Donelan directional spectra are close to those measured by Cox and Munk (1954). S ome discussionsare m