Abstract: The calculation of beam footprint position can be reduced by the actual complex sound speed profile (SSP) being replaced with the classic equivalent sound speed profile (ESSP), which is a simple constant gradient SSP. However, the positioning accuracy of ESSP decrease rapidly with the increase of the incident angle, and the bathymetry accuracy of the large incident angle beams (edge beams) will no longer meet the requirements of relevant measurement specifications. Especially in the uneven deep seafloor, it will lead to a non-negligible accuracy loss due to single equivalent SSP approximation. The research indicates that the positioning error of the ESSP shows an obvious quadratic function relationship with the angle for edge beams. Therefore, an error correction model based on the iterative calculation of the equivalent sound speed is proposed for inclined deep seafloor environment. The equivalent sound speed profile is calculated iteratively, while error correction of vertical distance and lateral distance of the edge beam is performed with an empirical error correction model. The simulation results show that the positioning accuracy of the proposed algorithm is same as that of constant gradient ray-tracking method, while the computational efficiency is improved by more than 29 times. This method has a quit benefit to the location of massive beam footprints in multi-beam sounding.