In order to study the variation law of steel box girder roof overpressure, flame behavior and steel box girder structure dynamic response under hydrogen explosion, a series of hydrogen explosion tests were carried out considering hydrogen concentration and ignition height. The high-speed camera was used to capture the flame behavior, the pressure sensor was used to measure the pressure inside the explosion container and the central roof, and the acceleration and laser displacement meter were used to measure the dynamic response of the steel box girder structure. The results showed that the evolution process of hydrogen deflagration flame acting on the roof could be divided into three stages: constant volume combustion stage, jet flame spreading stage and flame extinction stage. The flame length above the roof increases with the increased of hydrogen concentration. When CH2 was 16%~20%, three characteristic peaks Popen, Phel and Pvib appeared in the internal pressure curve, and two pressure peaks P1 and P2 appeared in the central roof pressure curve. When CH2 was 24%~36%, the characteristic peak Phel in the internal pressure curve changed to Pext, and a new characteristic peak P2 appeared in the central roof pressure curve, and the pressure peak increased with the increase of hydrogen concentration. The maximum overpressure of the inner and central top plates was the maximum at 200 mm ignition height. The dynamic response of steel box girder roof in the process of hydrogen explosion discharge could be divided into two stages: Quasi-static response stage and dynamic response stage, and the web plate was forced to vibrate under dynamic coupling effect. The peak acceleration of the central roof was the largest at 200 mm ignition height, and the peak acceleration of the web plate was the largest at 300 mm ignition height. With the increase of hydrogen concentration, the time when the central roof reaches the peak displacement was advanced, and the displacement amplitude increases.