Abstract: To investigate the dynamic characteristics of structures breaking through ice sheets and entering water, a series of vertical ice-breaking water-entry experiments were conducted using a water-entry experimental platform combined with high-speed photography. The experiments considered an ice-free condition and three ice sheet thicknesses equal to 1.5, 2.5, and 3.5 times the structure diameter (D0). The effects of ice sheet thickness on cavity evolution, ice failure modes, and motion characteristics of the structure were systematically analyzed. The results show that the presence of the ice sheet significantly alters the cavity evolution during water entry. The ice sheet accelerates cavity surface closure, suppresses radial cavity expansion, and promotes a rapid collapse of the cavity at later stages. When the ice thickness is 1.5D0, the cavity is able to fully envelop the structure, whereas for thicker ice sheets (2.5D0 and 3.5D0), the cavity fails to completely wrap around the structure. After the structure penetrates the ice sheet, conical craters are formed on both the upper and lower ice surfaces. For thinner ice sheets, the craters are symmetrically distributed around the penetration hole. In contrast, when the ice thickness reaches 3.5D0, an obvious asymmetry in crater geometry is observed due to the structure’s deflection during the ice-breaking process. Compared with the ice-free condition, the presence of the ice sheet leads to pronounced velocity attenuation and trajectory deviation during water entry. However, thicker ice sheets result in a reduction of the hydrodynamic resistance experienced by the structure in the subsequent underwater stage, indicating that the ice-breaking process plays a crucial role in modifying the downstream flow field and the overall water-entry dynamics.