Moving ships and other objects drifting on water often impact a bridge’s pile foundations. The mechanical model of the piles-bridge structure under horizontal forcing was established, and a time-domain ap-proach based on Finite-difference Method was developed for analyzing the dynamic response of the piles-bridge structure. For a single pile, good agreement between two computed results validated the present approach. The slenderness ratio of the pile, the pile2soil stiffness ratio and the type of the structure influence the dynamic response of the piles2bridge structure. The computed results showed that the stiffness of the structure deter-mines the dynamic response of the piles2bridge structure under horizontal forcing.