Abstract: In order to investigate the ballistic resistance and failure pattern of the casing with the impact of disk fragment,and find out structure optimization method,the phenomena of 1/3 disk fragment impacting on single and double layers plate target were simulated using nonlinear dynamical analysis software Dytran.Johnson-Cook material model was introduced for the disk fragment and the plate target,along with Gruneisen equation of state.Based on Lagrange method,impaction was simulated using explicit finite element method.Simulation results show that the major failure patterns of the plate target include plastic deformation,shear and tensile fracture,and that the single-layer plate has greater resistance than any other double-layered plates.Conclusions are also made that the ballistic limit velocity increases with the distance when it is beyond a certain value,and that the greater resistance is obtained in low or high proportion of the first layer with a constant of the total thickness.So,the resistance of double-layered plate targets may exceed that of the single plate,by reasonably arranging the thickness and the standoff distance of two plates.