Abstract: The 6.35-mm-diameter aluminum spheres were driven by a two-stage light-gas gun to normally penetrate aluminum sheets at the impact velocities of 2.23~5.26 km/s. The flash radiographs of the impact-induced debris clouds were presented and analyzed to describe the features of deforma-tion and fragmentation of the aluminum spheres. The propagation of the stress waves in the aluminum spheres was qualitatively explained, and the three statuses of spheres were observed under the different impact conditions. In the plastic deformation stage, the deformation of the aluminum spheres gets more distinct as the impact velocity and the sheet thickness increase. The critical impact velocity at which the principle part of the aluminum sphere began to shatter decreases with the increase of the sheet thickness, and this velocity is independent of the sheet thickness more than a certain value. In the complete fragmentation stage, with the increase of the impact velocity, the radial velocities and the fragment number for the principle part of sphere increase, and the fragment sizes decrease.