Abstract: By means of the island and cofferdam construction method, the ultra-deep foundation pit under ultra-deep soft soils in coastal areas is analyzed, based on the cross-sea tunnel project of the new campus of University of Macau on Hengqin Island. The design selection and construction method of the foundation pit are introduced. Based on the measured data, the deformation rules of foundation pit support system are discussed. It may offer valuable reference for the design and construction of ultra-deep foundation pits in coastal areas in future.