Abstract: Investigations of the response and failure of reinforced concrete slabs under projectile impact are of great significance in the safety calculations and assessment in protective engineering especially in nuclear containment structures. This paper presents a numerical study on the crack pattern of reinforced concrete slabs struck normally by a flat-nosed projectile at different velocities using a 3D meso-mechanical model. The model was developed based on the assumption that concrete can be considered to be a three-phase material containing cement mortar, aggregates and interfacial transition zone. By employing element reconstruction technique, difficulty in simulating very thin ITZ layer has been overcome. It shows that the failure patterns of the reinforced concrete slabs from our numerical simulations are in good agreement with available experimental observations.