The interactions between the excavation and surrounding environment and the influence of adjacent buildings on partial failure of support system are rarely studied and reported. Here, we studied the influence of excavation, partial failure of support and leakage of sandy soil behind the pile on the deformation coordination of the foundation pit and supporting system using model test of a foundation pit supported by internal retaining pile row system with and without adjacent buildings. The results show that affected by neighboring buildings, the horizontal displacement of the retaining pile parallel to the long side of the adjacent building increases with the excavation of the foundation pit, whereas that vertical to the adjacent building decreases. The axial force of the middle internal support increases greatly, followed by the angular support, while the side support decreases. The bending moment of the retaining pile parallel to the long side of the adjacent building increases, and the reverse bending point moves up, while that vertical to the adjacent building is quite the opposite. The ground settlement outside the pit caused by partial support failure is small, whereas that caused by continuous failure of the internal support is significant, and the influence range is 0.12-0.23 times of the excavation depth. The axial force of the adjacent intact support increases significantly, which can readily lead to progressive failure. The influence on the bending moment of retaining pile parallel to the long side of the building is greater than that vertical to the adjacent building. When the sand behind the pile leaks, the retaining pile parallel to the long side of the adjacent building decreases more significantly.