Seaquake is generally distinguished from tsunami. In this paper, the effects of seaquake on the floating structure is studied. At first the compressibility of the water and the effect of the free surface are studied to deal with seaquake phenomenon. Secondly, the dynamic pressure acting on the floating structure by seaquake is investigated, and it shows that the resonance plays an important role. In numerical work, the boundary value problem is solved by using Green function method. After computing the radiation hydrodynamic force and the vertical exciting force by seaquake, the structure's heaving motion is discussed.