Abstract: Based on the central-island and athwart construction method for excavation of large foundation pit of Shanghai South Railway Station of South Square in soft soil,the active mechanism of remain mound was analyzed;the deformation of underground diaphragm wall under the condition of three different remained mound width with or without consolidation was contrasted through centrifuge model test,the effect of remained mound width with or without consolidated on the deformation of diaphragm wall was acquired;then the deformation of underground diaphragm wall with several different widths of mound was calculated by FEM,finally it was presented that the reasonable mound width could be determined according to the diminishing ratio of deformation.