The relationship between the break-up of hypervelocity jets (> 4 km/s) and the decrease in penetration capability was addressed in this study. By applying a theoretical study, three cases were compared: when the jet was not broken, when there was a decrease in segment length after the jet was broken, and when the velocity gradient became zero after the jet was broken. The results showed that the decrease in penetration capability due to the break-up of the hypervelocity jet was due to the reduction in the length of the jet segments and the uniformity of the velocity after the breakup.