Abstract: Underwater explosions can cause significant damage to air-backed plates. In contrast to the effects of a single explosion, chronological secondary underwater explosions often result in more complex failure mechanisms within the structure. Under conditions of equal charge and detonation distance, this study employs an experimental approach, focusing on parameters such as deflection and strain induced by underwater explosions on the structure. It investigates the damage effects of chronological secondary underwater explosions and single underwater explosions on the air-backed plates revealing the damage patterns associated with sequential double underwater explosions compared to a single underwater explosion. The research findings indicate that when the plate frame damage mode involves large plastic deformation, under identical explosive charge and blast radius conditions, the secondary explosion significantly amplifies local structural damage. Damage parameters, such as deflection and strain, are considerably higher than those observed during the primary explosion. In extreme cases, the damage mode may differ, with the structure undergoing large plastic deformation during the primary explosion and subsequently developing a breach during the secondary explosion. However, a single explosion has a more noticeable overall damage effect on the structure, leading to greater overall deformation. Furthermore, the initial loading effect plays a significant role in the material strengthening response. Under identical loading conditions, the strain induced by the secondary loading accounts for 34.6% to 56.5% of that observed during the initial loading. The blast distance notably influences the effects of shock wave and bubble loading. In the case of contact explosions, structural damage is primarily driven by shock wave loading, with strain increment under shock wave loading constituting more than 90% of the total strain. As the blast distance increases, the impact of shock wave loading decreases, while bubble loading becomes more pronounced. Under the experimental conditions of this study, the strain increase caused by bubble jet loading can account for up to 60% of the total strain. The findings of this study provide valuable insights for mitigating the local damage effects on structures.