Abstract: From the spatial vector,comprehensively considering the effect of survey vessel attitude,sound velocity profile and seabed topography on incidence angle,the practical model for calculating multibeam seafloor incidence angle is derived.Based on Lambert law,the influence of seafloor incidence angle on backscatter intensity is corrected.The result shows that the proposed model can precisely calculate the beam incidence angle on the seafloor,and its influence on backscatter intensity is corrected effectively.