Abstract: The damage behavior of hydraulic structure caused by dynamic load attracts more attention at present, and is affected deeply by dynamic properties of the structure. In this work, the testing method of dynamic property of a gravity dam is studied by model test. The ambient vibration testing method was studied mainly and compared with traditional testing method. The experimental results show that ambient vibration testing method can measure the structural dynamic property effectively by structural dynamic response. The mode shape, frequency and damping ratio of model structure is affected lightly by magnitude of ambient excitation. The testing results of dynamic property of model structure are coincident by ambient vibration testing method and traditional testing method. The experimental results also show that ambient vibration testing method can detect the dynamic property of structural damage effectively. The experimental results verify further its effective to structural dynamic property of in suit detection based on ambient vibration.