Abstract: Wind energy is a new kind of inexhaustible energy. It is gradually replacing the traditional energy as its pollution-free and renewable. China has a long coastline, abundant offshore resources, and vast offshore space. Offshore wind farms have gradually become the focus of wind-power development. Large-diameter single-pile foundations are being widely used in the field of offshore power generation because of advantages including convenient manufacture and installation, clearer stress conditions compared with pile groups, and affordable cost and economy. Therefore, it becomes significantly relevant to study the dynamic response characteristics of large-diameter single-pile foundations under horizontal cyclic loads to eliminate the dangers hidden in engineering and installation and ensure normal usage during service. A numerical calculation model of an offshore, wind-power monopile foundation in heterogeneous soil was established by the finite element analysis software ABAQUS. The wave, ocean current, and wind load on the monopile foundation were equivalent to a bidirectional symmetrical cyclic load. The horizontal displacement, shear force, and bending moment along the pile shaft, and pile-side soil resistance under the horizontal cyclic load were studied. Furthermore, the horizontal displacements along the pile shaft under different cyclic times were compared with one another and analyzed. The results show that the horizontal displacement along the pile shaft accumulates gradually with time, and with increase in the number of cycles, the time lag of the maximum displacement of the pile body at mud surface occurs. The shear force along the pile shaft appears negative. The maximum bending moment of the pile body occurs in shallow soil. The variation in the soil-resistance curve of the pile body vs time occurs at a cut-off point at approximately 2/3 of the buried depth. Additionally, the variation laws of soil resistance within the upper and lower boundaries of the cut-off point are just the opposite of each other. The soil resistance increases significantly at the interface between silt and silty soil. The load along the buried depth of the inner wall of the pile remains unchanged at different time points.