In the area where groundwater is rich and has deep permeable layer, considering the construction difficulty and economic factors, the suspended water curtain is often used in the deep foundation pit. Based on the measured data of a deep foundation pit deformation in Foshan metro, this paper uses ABAQUS to establish a three-dimensional fluid structure coupling model, considering the actual working conditions of graded dewatering excavation, and study the deformation law of the suspended water stop curtain foundation pit in the excavation process. The results show that the deformation of diaphragm wall is bulging type with large deformation in the middle and small deformation on both sides. The maximum lateral displacement point is located near the excavation surface at each stage of excavation, and it tends to move downward with the increase of excavation depth. The top of the diaphragm wall is easy to deform towards the outside of the pit. With the increase of excavation depth, the maximum surface settlement point gradually away from the foundation pit. In the process of foundation pit excavation, the ground settlement caused by excavation disturbance of soft soil layer is decreasing, and the ground settlement caused by precipitation in the pit is increasing. The settlement caused by precipitation can reach more than half of the total settlement. Before and after reinjection, the distribution of surface settlement outside the pit is basically the same, all of them are groove type. The surface settlement deformation of suspended water stop curtain can be controlled to a certain extent by adopting reinjection measures.