Research on the wave dissipation performance of floating breakwater under long-period wave plays an important role in the engineering application of floating breakwater. Based on the open-source OpenFOAM，the RANS equation and SST k-ω turbulence model are used to simulate the flow field，and the overset method is used to simulate the interaction between wave and a floating breakwater. By transplanting and applying the MOODY library，a two-dimensional fluid-solid coupling double-pontoon numerical wave flume model is constructed. Through the verification of the existing physical model，the reliability of the model is proved. Then the comparative study on the wave dissipation performance of single-pontoon and double-pontoon is carried out，so the influence of wave height，number of floating breakwaters，the distance of floating breakwaters，and anchor chain stiffness on the wave dissipation performance of floating pontoon is studied respectively. It is concluded that：1）When the wave height increases，the wave dissipation performance of the floating pontoon will be improved. 2）To improve the wave dissipation performance，double-pontoon（or multiple pontoons）should be used as much as possible to shorten the spacing of the floating pontoons. 3）Increasing the stiffness of the anchor chain can also improve the wave-eliminating performance of the floating pontoons.