The experiments of the shielded charge initiated by the high speed half- prefabricated steel fragment has been studied in this paper. The damage way of half- prefabricated steel fragment to the shielded charge is hit, burning or detonation action. And the damage effect is structure damage or function damage. The result shows that toward Comp. B explosive with 1.62g/cm3 dense behind 6mm Q235 steel and of φ 200 mm×100mm size, the fragment’s critical detonation speed is about 2 400~2 600m/s.