Abstract: In order to reveal the mechanism of stress and deformation of the diaphragm wall under combined effect of dewatering and excavation, the processes of dry sand excavation and excavation with dewatering are carefully simulated by conducting a series of laboratory-scale 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 wall caused by excavation with dewatering is analyzed. 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 combined effect of dewatering and excavation compared with the case of dry sand excavation, and there would be no passive earth pressure zone in front of the wall, while the peak positions of lateral earth pressures behind the wall will move down. On this occasion, the diaphragm wall will develop greater bending moments and induce more significant lateral displacements of the wall.