Abstract: When a foundation pit is adjacent to the existing underground structures, the groundwater seepage and ground movement caused by dewatering will be blocked by the underground structures (i.e., the water- and soil-blocking effects). On this occasion, the deformations of the foundation pit with or without adjacent underground structures should be different. A pumping test is carried out based on an actual project, and the variations of water levels and the deformations of retaining walls and soils induced by pumping are measured. Thus, a three-dimensional fluid-solid coupling model is established to simulate the dewatering of a foundation pit considering the effect of adjacent underground structures. The distance between the foundation pit and the existing underground structures (D) and the dewatering depth (H_d) are selected as the two varying parameters in the numerical model to investigate the barrier effects of the adjacent underground structures on the deformation of the foundation pit caused by pumping. It is found that when D is small (e.g., D < 20 m), the soil-blocking effects play a leading role, reducing the ground settlement outside the pit (compared with the condition without the underground structures outside the pit). When D is large (e.g., D > 20 m), the water-blocking effects play a leading role, increasing the ground settlement outside the pit. However, with the further increase of D (e.g., D > 40 m), both the water- and soil-blocking effects gradually decrease, and the distribution of the ground settlement outside the pit tends to be similar to that without the underground structures. In the design of foundation pits, the coupling actions of the water- and soil-blocking effects of the adjacent underground structures should be considered so that more accurate calculation of the ground losses and wall deflections will be achieved, which is helpful to optimize the design of the foundation pits.