The present invention discloses a beach lateral erosion numerical simulation method based on a local grid adaptive technology, comprising steps of: (1) according to an initial slope shape of a known section, generating a large-range initial non-orthogonal grid system; (2) carrying out calculation according to a three-dimensional flow and sediment numerical model to obtain a vertical erosion and siltation thickness deltaZ and a transverse scouring value deltaW of a bed surface of a B point at the position of a slope toe of a slope; (3) according to a transverse scouring distance of the slope toe of the slope, moving a slope toe grid; (4) according to slope toe scouring information, judging whether the slope is instable and moving a slope top grid; (5) repeating the steps (2) to (4), and according to a newest slope toe position and position information of an adjacent grid node, determining a tracked grid; and (6) repeating the steps (2) to (5) so as to simulate the beach lateral erosion process of a river channel. According to the present invention, the difficult problems in the prior art are solved; in the whole calculating process, only the grid near the slope needs to be moved; accurate tracking and simulation of the process that slope retraction caused by beach lateral erosion are implemented; the defects of a conventional fixed grid and movable grid technology is made up; and an important technical method is provided for simulation of an alluviation flow river beach lateral erosion value.