Abstract: Explosively driven fragmentation of ductile metals is a very complex phenomenon in which the fragmenting material is plastically deformed. It is difficult to determine the characteristic of fragments produced by cylindrical casing with ends, and there are no corresponding theoretical analysis models. In the condition of near field explosion, the spatial distribution of fragments with powerful penetrability has influence on the fracture pattern of the structure. In this paper, the expansion and rupture process of warhead under the inner pressure of detonation products are simulated numerically. The spatial distribution and velocity characteristics of fragments produced by the warhead, and factors which influences the size of fragment are discussed. Furthermore, the results of fragment velocity obtained by numerical simulations and experimental results are compared. The results have revealed that the fragment with maximal velocity is produced by the far-end of warhead case. The difference among fragments mass along the axial direction is due to the length size, which is determined by the deviations of axial expansion strain rate. The relatively small deviations of axial strain rate, especially in the half part of the cylindrical casing far away from the initiation point, is probably the reason responsible for the massive fragments.