Abstract: The plain strain method often used in design, and the influence of space shape on the excavation foundation pit deformation was usually ignored to simplify design and research of foundation pit. Therefore, some economical wastes are caused. Based on numerical simulation methods, the influence of difference aspect ratio on foundation pit deformation has been investigated. The results show that, when L/B is less than 2, the retaining structure horizontal displacement and bottom upheaval deformation of foundation pit varies have obviously changed with the change of L/B, and when L/B is greater than 2, the change is not obviously and tends to a stable value. There is no obvious difference between 3D and 2D in computation when L/B is greater than 2. The displacement of foundation pit retaining structure in short edge and ground surface settlement of the pit soil in long edge have no obvious change with the change of L/B.