Abstract: A formula has been proposed to predict the ballistic parameter of projectile perforating concrete and steel composite target. Firstly, scale-reduced projectile perforation test on concrete slab with a rear steel linear was conducted. In the test, the ballistic parameters of the projectiles were measured. Secondly, based on the methodology that transforming the steel linear to an equivalent concrete slab with the same ballistic limit, the perforation model for thick concrete slab and classic formula for metal target against projectile were combined to assess the peroration resistance of the composite target. Finally, model predicted results were compared with the test data, which validated the analysis model.