The upper structure of high piled wharf in coastal soft soil area is loaded by waves or ships, which is transferred to the foundation soil through the pile foundation. The force is small and lasts for a long time, which causes the strength of saturated soft clay in the vibration range to decrease slowly, and the weakening effect of soil gradually accumulates, resulting in the horizontal displacement of pile foundation. In this paper, the maximum horizontal displacement and residual horizontal displacement of pile are deduced and calculated by the analytical method through appropriate simplification, considering the stiffness of pile group, plastic deformation of soil and cyclic weakening. A simplified calculation method of horizontal displacement of pile under horizontal cyclic load is obtained. Compared with the numerical simulation method, the results show that the simplified calculation theory of pile horizontal displacement under horizontal load can better reflect the displacement development law of pile, and then can predict the long-term deformation of pile.