Abstract: Offshore structures of a single pile are generally subjected to a variety of horizontal dynamic loads. In order to study the dynamic response of end-supported piles under horizontal dynamic loads on pile head, a three-dimensional water-pile-soil interaction system model is established. The pile and soil are assumed to be a linear viscoelastic media, and the water is assumed to be a linear acoustic media. Through the Helmholtz method for decomposition and separation of variables, an analytical solution is obtained for the resistance of the soil layer and water media to the water-pile-soil system. The displacement and horizontal dynamic complex impedance of the pile are then obtained in frequency domain based on the continuity conditions of contact interface between the pile and water and soil. The present solution is compared with the substructure method to verify the rationality of the method. Finally, the influences of water on the displacement response of pile top under different pile and soil parameters are studied. The results indicate that it is necessary to consider the water-pile-soil interaction in the design of the piles installed in offshore areas.