Abstract: A Kirchhoff-approximation numerical method of three-dimensional acoustic scattering from a rough underice surface is presented.Delaunay triangulation is used to triangulate a Gaussian rough under-ice surface,the Z-buffer algorithm is used to remove the surface elements in the shadowed areas and obtain those in the bright areas,and the scattering intensity is calculated by the planar element method of Gordon’s integration.In the numerical calculation model,the ice surface is regarded as one of local impedance,thereby incorporating it directly into the local reflection coefficient of the rough under-ice surface to calculate the scattering sound field and avoiding the approximation of the reflection coefficient in the analytical calculation model.The scattering intensities of the numerical and analytical models are compared for under-ice surfaces with large and small roughness and for different incident angles and frequencies.Of the two types of results,those of the numerical calculation model are more consistent with measurements.