Abstract: The local structures of the ships subjected to the severe wave slamming loads may experience large plastic deformation, which may threaten the ship’s structural safety. With the application of aluminum structures in high-speed ships and marine structures, the water impact of aluminum structures is gradually receiving widespread attention. In this paper, an aluminum scaled model based on the bottom structure of a real ship was designed, and then a series of drop tests of the aluminum stiffened plates with a deadrise angle of 0° were conducted at different drop heights to investigate the slamming pressure and structural dynamic elastoplastic responses. The test results show that the saturated impulse phenomenon also exists, and the final deformation of the stiffened plate is approximately linearly related to the drop height. The slamming pressure acting on the plate can be regarded as uniformly distributed due to the influence of the air cushion. Finally, the slamming drop tests were validated by adopting the explicit finite element technology based on the Arbitrary Lagrangian-Euler (ALE) algorithm, and good agreement between the numerical predictions and experimental results was achieved. The study provides experimental data on the aluminum stiffened plate structure design for high-speed aluminum ships and underwater vehicles.