Abstract: In this paper,the author has expounded .the basic theory concerning the mechanism of the strengthened saturated soft soils at the boottom of the deep foundation pit by dewatering, and the relevant formula is also introduced. By applying this theory to the engineering project of the deep foundation excavation for Shanghai New-World Building near the Shanghai Subway tunnel, the maximum horizontal displacement of the saturated soft soils around the deep foundation excavation is successfully limited to 0.12% H.