Abstract: Solitary waves and ocean currents are used to simulate extreme sea conditions, and the changing law of hydrodynamic characteristics of box-type main girder under different working conditions is investigated. Taking a coastal near-shore bridge as a model, using Fluent simulation software, based on SST k-ω turbulence model and VOF method, numerical simulation is carried out to simulate the role of wave current and bridge structure under various working conditions, and comparing the time course diagram of force, air-liquid distribution diagram, velocity cloud diagram of water quality points and so on, hydrodynamic characteristics of the box girder are analysed. The results show that: with the increase of forward relative flow velocity, the peak value of horizontal wave force on box girder gradually increases; the peak value of vertical force on box girder gradually decreases, and the corresponding time of peak value is advanced. With the increase of wave height, the peak wave force on the box girder in both horizontal and vertical directions increases, and the water level difference on the wave-facing side of the box girder cross-section brought about by wave impact increases, and the vertical slamming force on the wave-facing side of the box girder increases significantly.