In the combat operations of solid rocket engines, high-speed impacts from bullets and fragments are major threat source. They mainly induce mechanical damage into the engine casing and may further cause ignition, and detonation of solid propellants upon casing perforated. To study the protection performance of casing materials on solid propellants under bullet impact, the penetration experiments on by 12.7 mm armor-piercing incendiary bullets were conducted on two kinds of casing targets (D406A steel and aramid fiber) first. Further impact experiments on a casing-propellant combined targets were carried out by locating the high-energy propellant, represented by Nitrate Ester Plasticized Polyether (NEPE), behind the casing material. The research results show that compared with D406A steel, the aramid fiber casing exhibits better protective performance against high-speed armor-piercing incendiary bullets. In the tests of casing-propellant combined specimens, the protective effect of the aramid fiber casing is better than that of D406A steel, as it can effectively prevent the explosion of propellants and the generation of shock waves. This study provides an important experimental basis for the evaluation of the bullet impact safety performance of the casing-propellant system.