ABSTRACTHydroxyl‐terminated polybutadiene (HTPB) propellant faces the problem of aging from casting to use. Generally, the aging degree of HTPB propellant is evaluated by a destructive mechanical property test. Therefore, it is necessary to seek a new evaluation method. Electrical performance is a method that can achieve nondestructive testing. However, there are few studies on the electrical properties of HTPB propellant during aging. In this paper, the aging process of HTPB propellant was investigated based on volume resistivity, an inherent electrical property of materials that can reflect the obstructive effect of unit volume materials on current. It is concluded that the volume resistivity of HTPB propellant under aging at 70°C increases first and then decreases. The variation in internal structure during the aging of HTPB propellant was derived from the equilibrium dissolution method. HTPB propellant undergoes mainly post‐curing, oxidative crosslinking, and degradation chain‐breaking reactions during the aging process, with the occurrence of the first two reactions leading to an increase in volume resistivity, while the degradation chain‐breaking reaction is the opposite. Combined with the scanning electron microscopy (SEM) test, oxidizing substances test, and attenuated total reflection‐Fourier transform infrared (ATR‐FTIR) spectroscopy test, the changes of HTPB propellant in the aging process and the reasons for the change of volume resistivity were analyzed. The oxidative crosslinking reaction is the key step. This work provides new ideas for the subsequent realization of in situ nondestructive monitoring of HTPB propellant aging.