Abstract: When the tidal wave enters the trumpet-shaped estuary, due to the elevation of the terrain and the gradual narrowing of the estuary, a special hydraulic phenomenon of severe deformation will occur, that is, the tidal bore. Once the tidal bore interacts with water-related structures ( such as seawalls ), the tidal bore often propagates in the opposite direction under the obstruction of these structures, thus forming a backflow bore. Because of its great power, the backflow bore endangers people 's lives to a certain extent. In the past, there were few studies on the backflow bore, and the research on the mechanism of the backflow bore was not sufficient. In this paper, the hydrodynamic characteristics of the backflow bore on the vertical seawall are studied by high-precision numerical simulation, and the influence of the two main factors of the incident tide height and the initial water depth is analyzed in detail. At the same time, based on the one-dimensional continuity equation, the momentum conservation equation and the classical Bernoulli equation, the theoretical calculation formulas of the height of the backflow bore, the propagation speed and the impact load are derived. The accuracy of the theoretical calculation formula is systematically verified by the calculation results of high-precision numerical simulation. The results show that the incident tide height and the initial water depth have a significant effect on the height, propagation velocity, impact load and height of the backflow bore. The theoretical calculation formulas of the height, propagation velocity and impact load of the backflow bore proposed in this paper have high accuracy and meet the calculation requirements of the backflow bore analysis, which can be used in related engineering practice.