To maintain the natural ecological environment of the seas and islands，it is necessary to build a sea-linking structure on the dike. However，the construction of the structure is often affected and restricted by the geological and surrounding complex environmental conditions，leading to technical problems such as difficulties in structure selection and seepage prevention. Taking the remediation project of a sea island for the green petrochemical base in Zhoushan as an example，we study key technologies including structure selection，seepage prevention，structural calculation，and construction technology aiming at the complex conditions of the riprap foundation and the restricted sea environment，and propose an empty box structure plan for seepage prevention of punched plastic concrete piles and a construction plan for a temporary water-stop cofferdam with high-pressure jet grouting piles on a rock dump，which better solves related technical problems and may serve as reference for similar projects.