To establish the equivalent of perforating through ceramics and 603 steel, based on the residual penetration rule, the equivalent factor of the thickness ratio between 603 steel and ceramic impacted by rod armor-piercing projectile was introduced. The penetration process of rod armor-piercing projectile into ceramic composite steel and 603 steel was simulated with ANSYS/LS-DYNA finite element code, the numerical results corresponded well to previous experimental observation. The expression between equivalent factor and thickness of ceramic was presented through analyzing the numerical results. The basis of theory and data information for building the equivalent target of ceramic composite armor was provided in this paper.