In order to investigate the oxidation mechanism of solid propellant projectile on GH3044 alloy, the aperture in the GH3044 alloy lid was measured and analyzed by means of optical microscope, scanning electron microscope (SEM) and micro-hardness testing. The analysis results indicate that GH3044 alloy has endured a selective oxidation process along the grain boundaries at an oxidizing atmosphere, forming wedge-shaped inter-granular cracks. Therefore, an aperture in the lid was formed by the thermal stress as well as the metal oxide expansion stress. Moreover, the metal oxide (PbO) in the projectile reacted with the Ni-matrix, forming low-melting-point Pb-Ni eutectic, which is also supposed to be responsible to have accelerated the oxidation process.