Abstract: A subspace iteration method is adopted in order to acquire frequencies and modes of steel suspending cofferdam that is usually used in the construction of bridge pier.And also dynamic response of this structure under wind load is obtained using spectrum analysis method.The analytic results show that pulsant wind load has little effect on dynamic response of structure,then suggestions are made that during structure design gust response factor should be adopted to calculate the displacement response of steel suspending cofferdam.