The maximum excavation depth of one foundation pit in Henan Province is 5.8 m, the fields are mainly composed of saturated mucky silty clay, the minimum distance between the foundation pit and surrounding existing buildings is only 1.2 m, and I-steel cement soil mixing walls and prestressed bit expanded anchor are adopted to support the foundation pit. PLAXIS finite element software is used to numerical simulate the foundation pit supporting structure, and soil displacement, axial force and bending moment of I-steel cement soil mixing wall, anchoring force of prestressed bit expanded anchor and total multiplier are simulated and calculated. Some conclusions are drawn as follows: the simulated horizontal displacements of soils are near to the monitored data, which verified the rationality of FEM model of I-steel soil cement mixing wall; the deformation characteristics of structures and soils during the excavation of foundation pit are simulated reliably with the PLAXIS software, and PLAXIS is one appropriate method to simulate foundation pit engineering; the simulated and monitored horizontal displacements of soils, axial force of anchors, multiplier with strength reduction method during the excavation stages all meet with the requirement of foundation pit design; and so I-steel cement soil mixing wall is proved to be feasible for the foundation pit supporting engineering, so as to provide references for the similar engineering.