Abstract: In order to reveal the mechanism of stress and deformation of the diaphragm wall under combined effects of dewatering and excavation, the processes of dry sand excavation and excavation with dewatering are carefully simulated by conducting a series of laboratory model tests, and the data such as pore-water and earth pressures at both sides of the diaphragm wall, settlements outside the pit, bending moments and lateral displacements of the wall are collected. By comparing the characteristics of variations and internal connections of stress and deformation of the diaphragm wall under different conditions, the mechanism of stress and deformation of the diaphragm wall caused by excavation with dewatering is analyzed. The results show that the distribution patterns of lateral earth pressures at both sides of the diaphragm wall will be changed by both dewatering and excavation. The lateral earth pressures change more significantly under the combined effects of dewatering and excavation compared with the case of dry sand excavation, there will be less passive earth pressure zone in front of the diaphragm wall, while the peak positions of lateral earth pressures behind the diaphragm wall will move down. On this occasion, the diaphragm wall will develop greater bending moments and induce more significant lateral displacements.