Abstract: A mechanical model for a 3-dimensional beam-pier-pile system is proposed with finite element methods for a continuous rigid-frame bridge to analyze its vibration characteristics. The pile-soil system is simplified to build the space model and to calculate the dynamic behaviors of the system. Then the dynamic analysis model for the rigid-frame bridge is set up. The dynamic behaviors of the rigid-frame bridge are calculated and compared with different models, including that without considering the pile, that with pile base but without considering the effects of soil properties on vibration of the pile, and that with the interaction of the soil and the pile considered. The results show that the main factor affecting the third order frequencies are the properties of piles, but the properties of pile bases have not significant effects on the vibration characteristics of the beam-pier- pile system..