Abstract: Tidal bore is known for its high speed, high tidal level, and strong impact force. When tidal bore interacts with water-related structures such as seawalls and dikes, the obstruction caused by these structures leads to the reflection of the tidal bore, which forms a backflow bore propagating in opposite direction. The tidal level of the backflow bore is generally higher than that of the incident tidal bore, with a stronger impact force, posing a serious threat to coastal structures. To study the hydrodynamic characteristics of the backflow bore impact on bridge piers, a three-dimensional high-resolution numerical tidal bore tank is constructed based on the OpenFOAM two-phase flow model. The results show that when the tidal bore head contacts the bridge pier, a significant impact force is generated, and the force curve stabilizes after a brief fluctuation. After the formation of the backflow bore, its impact on the bridge pier is greater than the initial impact of the incident tidal bore head and generates typical K-H vortices in velocity shear layer. Furthermore, the maximum backflow bore force and impact pressure show a linear relationship with tidal bore height, while the variation in initial water depth has no obvious regularity. Finally, by combining the simulation results with existing theories, we derive a set of semi-theoretical and empirical formulas for the maximum backflow bore force and impact pressure based on corrected backflow bore height, propagation speed, and Froude number, aiming to provide a theoretical basis for the construction of bridges in areas where backflow bores are generated.