Abstract: In order to study penetration properties of high velocity fragment produced by underwater contact explosion, underwater ballistic experiments of 3.3 g cubic fragment was carried out, the results show that resistance co efficient of fragment is significantly influenced by the fragment shape. When the fragment crash on the steel plate, it will bring about great compress wave which makes fragment generate mushrooming and erosion, so the incident flow area increases and the weight decreases, consequently the underwater penetration ability of the fragments decrease with the increasing of velocity.