Abstract: The settlement of immersed tube tunnel is very important to its construction quality and safety. The definition and mechanism of instantaneous settlement of immersed tube tunnel are summarized by deep-water load plate tests, model tests and field measurements. The key influencing factors and mechanisms are demonstrated by combining the theoretical results of different pipe joints. Through the analysis of the monitoring data, the main role of instantaneous settlement in the settlement and its influences on the immersed tube tunnel are clarified. The research results may provide reference for the design and construction of immersed tunnel projects in the future.