Based on an extensive analysis on the design theory and construction of the dewatering of deep foundation pits, the paper establishes a 3dimensional finite element seepage model, accomplishes a 3dimensional finite element program and taking the dewatering of the Wuchang shield launching shaft of Wuhan Yangtse River Crossing Tunnel project as an example, makes relevant calculations. By comparing the calculation results of the water level lowering with/without pensile curtains with the measured data of the water level lowering with pensile curtains, the paper illustrates the effects of the pensile curtains on the dewatering of foundation pits.