Abstract: Based on the in-situ dewatering tests on phreatic water in an excavation of Tianjin Metro Line 3, it is found that considerable lateral inward displacement of diaphragm wall and the consequential ground settlement around the excavation occur during the dewatering of phreatic water before its construction. Further field measurements indicate that the magnitude of the lateral displacement of diaphragm wall can be significantly reduced by applying struts at the top of wall before its construction and by staged dewatering and in the meanwhile, the pattern of displacement is transformed from cantilevered to bulged one in the middle of wall. Then, three-dimensional fluid-solid coupling numerical analysis is performed to simulate the field dewatering tests, and the mechanism of the lateral displacement of wall induced by dewatering of phreatic water before excavation is studied. Numerical results show that the soils inside the excavation are consolidated in three-dimension during and after dewatering, leading to the redistribution of earth pressure between the wall and the soils. The displacement of diaphragm wall can be effectively reduced by the installation of the first level of struts and staged dewatering.