Abstract: Offshore bridges are threatened by extreme wave conditions such as tsunamis, where the colossal wave forces can severely impact the superstructure of the bridge. To simulate the impact characteristics of offshore box girder bridges under the action of tsunami waves more realistically, the experiment utilizes solitary waves to simulate tsunami waves. Using a domestic offshore box girder bridge as the background, a bridge model with a scale ratio of 1∶25 is employed to conduct tsunami wave impact experiments. The study investigates the pressure and flow field characteristics at different positions on the box girder under various tsunami wave conditions. Firstly, the effect of wave generation is verified by comparing with theoretical wave heights. Secondly, the impact of piers on the tsunami-induced pressure on the box girder and the analysis of the force mechanism of the box girder are carried out. Lastly, the influence of solitary wave height and impact submersion coefficient on the forces acting on the box girder is analyzed. The research indicates that the range of influence of the piers on the box girder is consistent under different conditions, but the degree of influence varies significantly at different locations, with the pressure at the middle bottom of the beam significantly higher than other positions (difference reaching 16%), showing a significant impact of piers on the pressure distribution of the box girder. When the water level is low (not submerging the top of the pier), the duration of tsunami impact is positively correlated with the wave height, while at high water levels (submerging the pier top), the effect is reversed. The impact of solitary waves on the box girder is complex and variable, influenced not only by the wave height and impact submersion coefficients but also by the structure and position of the beam. Therefore, these factors should be considered comprehensively when designing and evaluating similar structures.