In order to improve the anti-explosion protection performance of ships and explore the damage mechanism of marine sandwich structure under impact load, the close-range air explosion test of U-shaped folded sandwich plate was designed and carried out. The deformation and failure mode of the sandwich plate under shock wave load were analyzed, and the finite element simulation analysis was carried out. On this basis, the damage characteristics of sandwich plates under the combined action of shock wave and fragments were studied by prefabricating fragments at the bottom of explosives. The influence of panel thickness and detonation distance on the anti-explosion performance of sandwich plates was discussed from three aspects: panel break size, vertical displacement and energy absorption. The results show that the failure modes of the upper panel of the sandwich plate under the combined action of shock wave and fragment are large deflection, boundary tearing, plug break and scattered perforation. The bottom panel is dominated by large deflection and pits, and the shape of the upper panel break changes from' butterfly' to' circular' with the increase of the thickness of the upper panel. At this time, the upper panel and the core layer are the main energy absorbing components. The deformation of the central region of the sandwich plate is more sensitive to the decrease of the detonation distance, while the deformation of the edge region has no significant change. The total energy absorption of the sandwich plate, the energy absorption and proportion of the lower panel and the core layer increase with the decrease of the thickness of the upper panel. The change of the thickness of the lower panel and the core layer has little effect on the overall energy absorption of the sandwich plate and the proportion of each part.