Abstract: Most of the bridge failures are caused by scour which can increase the scour depth at piers and reduce the bearing capacity of the bridge foundation. In the simply supported bridge-piers-soil system, the overall stiffness of the system is directly affected by the bareness degree of the pile, and thus it has an influence on the modes of the system. Based on the numerical simulation of the dynamic model for a three-span simply supported bridge, the scour depth at piers and the dynamic characteristics of the bridge are discussed, and the variations of dynamic characteristics, especially the modal frequencies of the bridge at different scour depths and scopes, are studied as well. The research results are helpful for the nondestructive examination of the scour depth of bridge foundations.