Using relaxation spectrometry methods, the features of formation of interfacial layers in polymer composites based on 5-211-BN epoxyanilinophenol formaldehyde binder reinforced with CBM high-modulus aramid fibers are studied. The cases of the initial unmodified and modified neutralization of the surface of the reinforcing filler under loading in various temperature-time regimes are considered. It is shown that the used set of relaxation spectrometry methods allows one to evaluate the features of formation and the structure of interfacial layers in polymer-polymer systems. It is established that the morphological structure of the interfacial layer is strongly dependent on the chemical nature of the components and on the intensity of their interaction.