To explore the high-velocity-penetration resistant mechanism of ceramic/thin steel composite targets (hereafter called CS targets), the failure modes and penetration resistances of CS targets with 3 mm-thick SiC ceramic layer and 0.6 mm-thick steel layer were analyzed through ballistic tests, and compared with the monolithic steel plates of identical areal densities. Based on the energy conservation principle, a theoretical prediction model for high-velocity penetration of CS targets was established. Comparison between predictions and testing results was conducted. Results show that the failure modes of rear thin steel layers in CS targets change from shear plugging to petalling due to the existence of front ceramic layers, which greatly promotes the anti-penetration energy-absorption efficiency of rear thin steel layers. Therefore, the overall penetration resistances of CS targets are superior to and above 15% higher than the monolithic steel counterparts. The predicted residual velocities of projectiles after perforation of CS targets correlate well with those experimental results, and the relative errors are all within 5%, which proves the rationality and validity of present theoretical mode.