［Purposes］ The paper aims to study the deformation evolution law of the excavation of huge deep foundation pits in complex environments and optimize the design of support structures.［Methods］ Based on the foundation pit engineering of Guangzhou Metro Line 11, the variation laws of the horizontal displacement of support structures and the surface settlement of the surrounding soil were studied by using the finite-difference software FLAC^3D in the foundation pit excavation project. By analyzing the influence of the embedded depth, the thickness of the diaphragm wall, and the number of layers of support structure on the deformation of the foundation pit, the support structure of the foundation pit was optimized. The support effect before and after the optimization of the support structure was compared and analyzed.［Findings］ Under different operating conditions, the surface settlement of the surrounding soil first increases and then decreases, and the largest settlement occurs at the position of 15.0 m from the edge of the foundation pit; Under different embedded depths, the variation trends of the horizontal displacement of diaphragm wall and the surface settlement of surrounding soil are basically the same; The change of the thickness of diaphragm wall has no obvious effect on its horizontal displacement and surface settlement; The increase of the number of support layers can significantly reduce the horizontal displacement of the support structure and the maximal settlement of the surrounding soil. After the optimization of support structures, the maximal settlement of the surrounding soil is reduced by 23.88%, and the maximal horizontal displacement of diaphragm wall is reduced by 1919%.［Conclusions］ In the design of the same type of foundation pit, attention should be paid to the selection of the number of support layers. The thickness of support structure can be appropriately reduced if necessary.