Aiming at the characteristics of a large-scale reclamation project of offshore islands and reefs，such as large scale，heavy wind and waves，complex geological conditions，and urgent land demands，the key technologies of reclamation engineering are studied. Based on the reclamation project of the Zhoushan green petrochemical base，and the analysis of project scale，hydrological characteristics，geological conditions，and construction period requirements，we summarize the key technical problems of diking，seepage control，cutting mountains，reclamation，and foundation treatment，and propose the solutions to the key technical problems such as blasting silting，foundation seepage control，rapid land formation，and settlement control，then verify the treatment effect of key technical problems combined with the implemented projects. The research guides for the design of large-scale reclamation of offshore islands and reefs.