Abstract: Taking a deep foundation pit accident supported by soil-nailing wall and cantilever piles as an example, the scheme of the original design and reinforcement design for its first reinforcement is introduced. The causes of the accident are analyzed from the aspects of design, construction, management and so on. The scheme of secondary reinforcement design for this project is proposed. The method for the design of secondary reinforcement of the foundation pit and the key points are discussed. Some useful conclusions are drawn for similar projects as a reference.