Abstract: Instability risk assessment is an important link of design and safe construction of excavations. Firstly, based on a comprehensive analysis of risk events and their risk factors for excavations with cantilever retaining , a comprehensive analysis model of instability risk for excavation engineering is formulated considering the risk probability and risk consequence. Secondly, considering the mechanical mechanism of instability of excavations and the interval uncertainty feature of physical and mechanical parameters of soil, a method to determine the risk probability of foundation instability is presented by introducing the non-probabilistic reliability analysis. Thirdly, based on the information entropy theory, the evaluation method for the risk consequence is formulated, which can reflect the experts’ evaluation level. And the improved risk matrix method of instability risk for excavations with cantilever retaining is developed. Finally, the method is used to analyze the practical engineering, and it is shown that the proposed method is feasible and reasonable.