The remote laser method is considered based on determination of the difference of phase incursion in a film at sounding wavelengths and intended for measurements of thin film thickness on a rough sea surface. Mathematical simulation demonstrates that the method permits one to measure film thickness of units and tenth parts of micrometer by sounding at close wavelengths. For a collection of wavelengths: 0.767, 0.800, 0.792, and 1.600 μm, the range of measurements of film thickness is 0.1-6.4 μm. Mean error in determining film thickness in most cases is not worse than 5% for a series of 30 measurements and root-mean-square value of measurement noise of 1%.