The composite structure of shell and skirt of solid motor is aging during long-term storage, which adversely affects the reliability of shell structure. The microstructure parameters of the epoxy resin at the interface of the composite structure were characterized and compared with the results of macroscopic mechanical properties. The results show that in the process of accelerated aging, the surface of epoxy resin matrix first appears small grooves, resulting in chemical aging of the material surface embrittlement, toughness reduction, surface gullies increase, and surface roughness increase. Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) reflected the molecular level damage of the epoxy resin matrix. With the extension of aging time, the chemical reaction between the element groups was observed. Meanwhile, the change of element content indicated that oxidative crosslinking or oxidative decomposition reaction might occur during the accelerated aging process. The change of the characteristic parameters in the accelerated aging process is related to the decline of the mechanical properties of the materials.