The construction of offshore platform structure has long period and high cost in the construction of diaphragm wall in sea.To solve the problem,the combined cofferdam of locking steel pipe pile and I-shaped sheet pile is used to built islands in the sea,and the parallel steel wire cable is set outside the cofferdam for flexible restraint,forming a flexible composite cofferdam structure of “lock steel pipe pile+I-shaped sheet pile+parallel steel wire cable” in the sea.Compared with traditional rigid hoop and the non-hoop composite cofferdam structure,based on field monitoring data,stress and deformation characteristics of the proposed flexible hoop composite cofferdam structure are analyzed.The results show that compared with the conventional rigid hoop structure,the maximum bending moment of the pile in the flexible hoop structure is reduced by about 50% under the same dredger fill pressure load.The maximum horizontal displacement of the pile top is too large without the hoop structure.Under the action of uneven loading,the stress of the rigid hoop will change abruptly,while the flexible hoop is always tensioned and the stress is evenly distributed.The monitoring results show that the measured stress and deformation of the flexible composite cofferdam structure are in good agreement with the calculation.