This study presents a numerical investigation of dewatering-induced settlement and wall deflection during pumping tests in Tianjin, China. Based on the measured groundwater head and building settlement during the pumping test, a three-dimensional liquid–solid coupling model is established by using the finite element method (FEM). The void ratio, hydraulic conductivity, and elastic modulus of each layer are back-calculated through the numerical model. The groundwater drawdown, seepage field, ground settlement, horizontal ground displacement, and diaphragm wall lateral deflection are analyzed using the FEM model. The simulated results demonstrate that (i) the maximum ground settlement outside of the excavation reaches to 82 mm due to the leakage effect of aquitards; (ii) large horizontal displacement occurs in the soil during the pumping test with a maximum value of 28.3 mm, and the installation of the diaphragm wall in the aquifer can reduce the horizontal displacement of the ground; (iii) long-term pumping causes a large lateral deflection of the diaphragm wall, and a maximum value of 23.2 mm occurs at the layer where the screens of the wells are located; and (iv) long-term large-scale pumping should be avoided before excavation.