It is very necessary to predict the residual velocity of a projectile after perforating a concrete barrier for the protective structures. In this paper, projectile perforation test on the thin 128.4 MPa ultra-high performance steel fiber reinforced concrete (UHP-SFRC) slabs was conducted, in which the diameter of projectile was 25.3 mm and the thicknesses of slabs ranged from 40 mm to 100 mm. All the slabs were perforated normally and the projectile residual velocities were captured by high-speed camera. To assess the projectile residual velocity, a semi-analytical projectile perforation model for thin concrete slab (H/d ≤ 5) was established, which completes our previous work [Peng et al., 2015] for thick slab (H/d > 5) within a unified framework. The proposed model was validated by the present and existing available perforation test data on thin concrete slab. Furthermore, the unified model was employed to evaluate the impact resistance of spaced segmented concrete slabs and good agreements were achieved.