Abstract: The Kirchhoff approximation method with modified reflection coeficient is used to calculate the threedimensional acoustic scattering of Gaussian rough under-ice surface.The concept of local statistical average reflection coefficient of under-ice surface is proposed in the calculation model.The scattering sound field of two-dimensional Gaussian rough under-ice surface is divided into coherent scattering and incoherent scattering.The scattering cross coefficient formulas of two kinds of scattering components are derived respectively,and the three-dimensional scattering intensity is obtained.The relationship between scattering intensity with RMS height of Gaussian rough under-ice surface,incidence angle and frequency of sound wave is analyzed.The scattering intensity of Gaussian rough under-ice surface is measured in the laboratory water tank,and the calculation results of the theoretical model are verified.The experimental results are compared with the theoretical calculation results of the local statistical average reflection coefficient of underice surface in this paper and the mirror reflection coefficient of under-ice surface in the literature.The calculated results of the local statistical average reflection coefficient are in good agreement with the experimental results.