Abstract: A model for predicting the ballistic limit velocity was developed by combining Florence's model with the plug equation for the projectile penetration into sheet, The effects of structure parameters, including facesheet thickness, ceramic core thickness and back plate thickness, on the ballistic limit velocity of steel/ceramic/steel composite armor against 7.62 mm plain steel projectiles was investigated to optimize the armor structure and identify the validity of the model analytically and experimentally. The results reveal that the model is in good agreement with experimental values, with the relative error less than 15%, and it is optimum as the thickness ratio of ceramic tile to steel back sheet is between 1.5 to 4.5.