A 3D-FEM model involving the dynamic interaction of large diameter monopile and soil was established with the Abaqus software based on the elastic half-spacetheory. Then, the coupled horizontal-rocking vibration of monopilehas been analyzed. The influence of the dimensionless frequency, pile length-radius ratio, pile thickness-radius ratio, pile-soil elastic modulus ratio, scour depths around the pile to the dynamic impedance of the pile are discussed and the results are nondimensionalized to improve its applicability, which show that the influence of dimensionless frequency on the dynamic characteristics is closely related to other factors. Meanwhile, the pile length-radius ratio, pile-soil elastic modulus ratio, pile thickness-radius ratio, and scour depths around pile have a great influence on the dynamic characteristic of monopile. The study also found that the stiffness increases with the increase of length-radius ratio and there is a certain critical pile length. Damping has the same trend in a low dimensionless frequency. When the scour depth around the foundation reaches two times the diameter, the stiffness of the foundation will drop to about 1/3 of original value and the decrease of damping is also very significant.