During the process of implementing central island scheme and constructing multi-span structures in large foundation pit projects, due to the limited construction conditions, the support system generates unbalanced soil pressure, which is transmitted inwards through the support in terms of horizontal lateral force. It has been designed to apply horizontal lateral forces to the existing structural system of the basement, which was jointly undertaken by the beams, columns, and engineering piles of the underground structure. In this case, the structural components near the load-bearing end is expected to exhibit significant internal forces and structural deformation. Therefore, under the condition of large horizontal lateral forces, it is necessary to propose practical and effective strengthening measures to improve the stiffness of the load-bearing end structure and control the deformation within a reasonable range. Taking an engineering project as the background, simulates and discusses the horizontal lateral force resistance of multi-span structures in deep and large foundation pits through three-dimensional numerical analysis. Several structural strengthening schemes are compared and selected. The results show that the design of slant support compression bar strengthening at the loading end of the system can effectively improve overall ability to resist horizontal lateral force.