Based on the three-dimensional potential flow theory, the double-cylinder floating breakwater with good wave breaking performance is taken as the research object, and the wet surface model of the floating breakwater under the action of irregular waves is established by finite element software Workbench. The frequency-domain hydrodynamic performance analysis and time-domain analysis on floating breakwater is preformed by the hydrodynamic analysis software AQWA. The response amplitude operator (RAO), motion response and mooring line tension of the floating breakwaters under extreme sea conditions are focused on, which provides reference for the related practical projects.