To improve the horizontal vibration theory of tapered pile for better use, based on the Timoshenko beam model, the horizontal vibration problem of tapered pile embedded in viscoelastic foundation subjected to horizontal harmonic excitations was investigated. First, the Winkler foundation model and Timoshenko beam model were used to simulate the viscoelastic foundation and tapered pile, and the lateral coupling vibration model of pile-soil system was established. Then, the analytical expressions for the horizontal displacement, bending moment, and shear force of the tapered pile were derived by means of variable separation method and transfer matrix method. The influence of the design parameters of pile-soil system on the horizontal vibration characteristics of tapered pile was analyzed based on the obtained solutions. Finally, the results were verified by comparing with the Euler beam model solutions, and the difference between the solutions of the two models was analyzed. Research results show that the dynamic response of the pile top was little affected by the variation of the wedge angle. The dynamic response of the whole pile increased with the increase of the pile-soil stiffness ratio. With the increase of the dimensionless frequency, the horizontal displacement of the pile decreased gradually. Although there were differences between Timoshenko beam model and Euler beam model under small length-diameter ratio, wedge angle had basically the same effect on these two models.