As extreme weather becomes more frequent and intense, cross-sea transportation infrastructures face a greater risk of flooding, which leads to economic loss and threats to life. The artificial island of the Hong Kong-Zhuhai-Macao Bridge is a crucial hub connecting the undersea tunnels and bridges. Heavy rainstorms could cause flooding of the artificial island, which threaten the safety of traffic and pedestrians on the island. It is significant for simulating flooding and assessing danger for pedestrians on islands, where people are difficult to rescue if flooding occurs. In this study, a coupled flood model is proposed to simulate the rainstorm-induced flood, and a stability model in floodwater is used to evaluate the danger degree of pedestrians on the artificial island. The drainage network and surface flow models are coupled to establish a flooding disaster model for the island. The results indicate that the turning of secondary roads on the island is more susceptible to flooding under extreme rainfall conditions. The map of pedestrian danger presents that the road turnings and main road are dangerous locations during the flood. The method proposed could offer technical support for safety management and flood prevention of cross-sea transportation infrastructures.