The optical wave scattering from the slightly rough surface of three-layer medium is studied. The formulaes of the scattering coefficients for different polarizations are derived using the small perturbation method. A Gaussian rough surface is presented for describing rough surface of layered medium, the influence of the permittivity of layered medium, the mean layer thickness of intermediate medium, the surface roughness parameters and the incident wavelength on the bistatic scattering coefficient of HH polarization are obtained and discussed by numerical implementation.