Abstract: Steel-concrete composite structures have significant application value and development potential in the construction of very large floating structures. In order to overcome the shortcomings of conventional very large steel or concrete floating structures, a new type of steel-concrete composite pontoon-type floating structure was proposed, and its overall design procedure was presented. To carry out the hydroelastic analysis required in the design procedure, a three-dimensional hydroelastic package THhydro was developed based on the open-source hydrodynamic package NEMOH to analyze the hydroelastic performance of very large floating structures, and the program was verified by the previous experiments conducted by Yago and Endo from Japan. What is more, based on the hydroelastic analysis and structural strength analysis, a case design of a steel-concrete composite pontoon-type floating structure was conducted, and the design result of the composite structural scheme was also compared to that of a conventional steel structural scheme. The calculation results have proved that:the application of composite structures to offshore very large floating structures is feasible. Compared to conventional steel structural scheme, the proposed composite structural scheme can greatly reduce the steel consumption when designed under the same draft and stress level. The ratio of steel to concrete significantly influences the indexes including the structural loading capacity and steel consumption. The contribution of the wave effect accounts for 20%~60% percent of total structural response, which indicates that a reliable hydroelastic analysis is very important for the design of very large floating structures. Finally, some further research prospects of very large steel-concrete composite floating structures were discussed as well.