The settlement of pile foundation of a bridge can affect the safety of the bridge itself and the vehicles on the bridge. However，the complexity and variability of pile foundation as well as the randomness in construction make it uncertain to identify the settlement of pile foundation. Based on large diameter pile foundation of a bridge，it utilizes the elastic-plastic FEM to analyze the factors that affect the pile settlement，such as the pile-side soils，pile-end soils and the characteristics of the pile-soil interface. The soil constitute is assumed to be Drucker-Prager elastic-plastic model，the concreted pile shaft is considered as the linear elastic model and the soil-pile interface is monitored by contact elements. The results show that the pile foundation design for this bridge is reasonable with enough safety potential. Moreover，pile-side soil is the most sensitive factor to affect pile foundation settlements，and then is the pile-end soil. In engineering practice，improving the strength of pile-side soil，properly selecting support layer and avoiding destroying the strength at the pile-soil interface are the effective measurements to decrease the pile foundation settlements, ensuring the superstructure's safety.