In this paper, the floating breakwater structure is simplified to a rigid body motion with two degrees of freedom, a two-dimensional numerical flume is established using the computational fluid dynamics software Star-CCM+ based on the theory of viscous incompressible fluid, the free surface is captured by the volume fraction method, the overset mesh technique and the finite volume method are used. A new proposed box-type floating breakwater with wing baffles and a traditional box-type floating breakwater without wing baffles are simulated numerically, and the wave attenuation performance, motion response and flow field characteristics of the two types of floating breakwaters are compared and analyzed. The results show that: wing baffles can effectively reduce the motion response of floating breakwater; the asymmetry of the motion response of the floating breakwater with and without wing baffles is caused by two pairs of vortices with different strengths and evolutionary forms underwater; the additional wing baffles can induce stronger vortexes underwater, thus absorbing more wave energy, which can significantly improve the wave attenuation performance of the box-type floating breakwater; the additional wing baffles have a great potential in the design of high performance floating breakwaters.