Abstract: How to assess the impact of construction of deep excavations on adjacent structures effectively and to evaluate the influence of each risk factor is one of the most urgent problems during the pre-construction period. First of all, the impacts of construction of deep excavations on adjacent buildings are analyzed. The geometric adjustment factors of the probability are given according to the relative position between piles and excavation. Secondly, combined with the construction status of deep excavations in soft soil area, the risk factors which cause buildings to tilt even collapse are analyzed. On this basis, a fault tree for building accidents is constructed. Finally, based on the probability and consequences of accidents, the security level of buildings is given. The weight of each risk factor can be obtained by importance analysis.