Abstract: For fast calculation of high-frequency sound scattering from undulating sea surface, an improved Kirchhoff approximation method is proposed. The method considers the multiple-scattering sound field between the shadow area and the bright area of the sea surface, and can calculate the scattering sound field of the rough sea surface at small incident angles. The accuracy and applicability of the proposed method are verified by taking the finite element calculation results of sound scattering from one-dimensional cosine and Gaussian sea surfaces as standard solutions. This method is used to calculate the scattering intensity from one-dimensional cosine sea surface, analyze the distribution of sea surface scattering intensity at different frequencies and angles of incident acoustic wave, and explain the generation mechanism of Bragg scattering. At the same time, the variation law of the scattering intensity from Gaussian spectral sea surface is discussed under the conditions of different root mean square heights and correlation lengths of sea surface.