Abstract: The Underwater Three-dimensional imaging sonar based on the Conventional Beamforming suffers from fat beams and high-level sidelobes.The two-dimensional decovonvolved beamforming algorithm is proposed to improve the imaging resolution of three-dimensional imaging sonar.The algorithm completes the planar array beamforming for all distance slices,and realizes the near-field planar array beamforming using Fresnel approximation.Then,the twodimensional deconvolution techniqueis applied to the beam power to obtain high-resolution and suppress the sidelobe level caused by the beam response which is non ideal impulse function.The computer simulations demonstrate that the proposed method is efficient to enhance the spatial resolution and suppress the sidelobe level of the underwater 3D imaging,at the same time,to retain the robustness like conventional beamforming at wideband and different array aperture conditions.Through the experimental study of the prototype,the spatial resolution is increased by one time and the sidelobe level is reduced by 20 dB using the proposed method.