Abstract: The diffusion behavior of H₂O and O₂ in T313 was studied by molecular dynamics simulation. The binding energy and interaction mechanism between different interfacial layers of PU_PBT/T313/AP composite systems were studied. The diffusion simulation results show that the diffusion coefficient of H₂O in T313 gradually decreases with the increase of temperature. In contrast, the diffusion coefficient of O₂ in T313 shows an opposite trend to that of H₂O, suggesting that the diffusion phenomena of polar molecules and non-polar molecules in the bonding agent membrane are distinct. After adding the bonding agent T313, PU_PBT binds more tightly to AP particles. The interface adhesion ability of PU_PBT/T313 system is mainly pinpointed by strong van der Waals and hydrogen bonding interaction between the atoms in the PU_PBT system and those in the T313, while that of T313/AP system by strong van der Waals forces between ammonium perchlorate and the atoms in the PU_PBT system.