This research is carried out with the tunnel across Yangtze river in the south-bank at Weisan road in Nanjing as the background. In the light of the engineering geological and hydrogeological conditions in the site area, and with reference to experiences in similar projects in Nanjing, the radius of area affected by the dewatering and the comprehensive permeability coefficient of the site area were determined. On this basis, the calculation and design of dewatering for the foundation pit were carried out, and the applications of dewatering wells and buck wells in foundation pit dewatering were introduced. Furthermore, a numerical model of groundwater seepage was established to simulate and validate the dewatering effect for confined aquifer in the foundation pit by using 3-D finite difference method. The simulation results and practice both show that the dewatering scheme is reasonable and feasible.