Abstract: According to analysis of the phenomenon of internal erosion of soils, the phenomenon of internal erosion of soils is that some soil particles departing from soil skeletons become fluidized ones sharing the same velocity with fluid phase. A physical model for the internal erosion of soils is established, and the correspoding constitutive equation is given. The land subsidence caused by the internal erosion of soils owing to pumping confined groundwater is discussed during the construction of third-class deep foundation pits. The numerical model depends on a practical deep foundation pit consisting of 8 layers of soils of Shanghai area. Based on the mathematical-physical model, four governing equations and the finite element numerical method, the calculated results demonstrate that the internal erosion will cause additional land subsidence and deformation.