The shell model of fragment penetration is built by finite element analysis software ANSYS/LS-DYNA to study the penetration effect of G45 steel fragments with different qualities on medium and large caliber ammunition shells. The ammunition shell is changed into a Q235 steel plate by the equivalent formula， and numerical simulations of the penetration of the equivalent target plate Q235 steel by G45 steel fragments with different qualities at different speeds are carried out. The simulation results show that under the same mass， the penetration depth and diameter of G45 steel fragments impinging on the target plate increase with the rising velocity. The small mass G45 steel fragments of 4.7 g and 9.8 g cannot penetrate the equivalent target of medium and large caliber projectiles in the velocity range of 800–1800 m/s. The limit penetration velocity of 19.5 g G45 steel fragment penetrating the equivalent target of 20 mm medium and large caliber projectiles is between 1 200 and 1 400 m/s.