Abstract: The armor-piercing effect regarding tungsten alloy fragment on the finite thickness steel and aluminum plates was researched. The experiment system using by 12.7 mm smooth bore ballistic gun, 57.5 mm/14.5 mm two-stage light-gas gun and velocity measurement equipment was setup. A series of terminal ballistic experiments with the 3g (diameter 7 mm) spherical tungsten alloy fragment against different thickness metal plates, including the thickness of 9.64, 11.78, 14.81, 15.89, 17.9 mm Q235A steel plates, and the 10.16, 20.38 mm 2A12 aluminum plates, were performed to get the ultimate pierced thickness. In addition, the micro structure characterizations of the residual penetrator were analyzed by scanning electronic microscopy (SEM), and the failure mechanism of tungsten alloy fragment under different conditions were obtained. At the same time, the numerical simulations with the same projectile-target action systems were performed, and the simulation results have good agreement with experimental data. The resistance variation properties of the fragment against metal plate were obtained. The high density of steel plate should be the main reason for the ultimate pierced thickness. The research results will be an important reference for further research on related issues.