Based on the structure of traditional small caliber APDS (Armor Piercing Discarding Sabot), a novel reactive core projectile (RCP) is proposed to improve the damage capability against fuel tank. The penetration processes of RCPs impacting partially filled fuel tanks with different penetration angles are investigated by numerical simulation, in which the Powder Burn model is adopted to describe the unique impact-induced delayed deflagration behaviour of reactive material. The simulation results show that, compared with the inert projectile, the RCP not only releases additional chemical energy during penetration process, but also increases the proportion of kinetic energy transferred to the surrounding fuel, resulting in the enhanced damage to fuel tank. Moreover, the damage effect of RCP is significantly influenced by the penetration angle, and a relatively small penetration angle is beneficial to improve the damage effect. The simulation results verify the time sequenced combined damage mechanism of kinetic energy and chemical energy of RCP, which provides a beneficial reference for the design of small caliber APDS.