Abstract: The composite system of 3,3-bis(azidomethyl)oxetane-tetrahydrofuran copolymer/ammonium perchlorate PBT/AP/additives and the bulk phase model of PBT with integrated additives were selected as research objects to explore the influence mechanisms of grafting densities and temperature on the microstructure and performance of PBT/AP/additives composite systems. The spatial density distribution, diffusion behavior and motion trajectories of three small-molecule additives (TDI, TEA and TMP) were analyzed systematically. Results demonstrate that TDI is mainly distributed in the regions at approximately 1~2 nm and 3~6 nm from the AP surface, TEA is concentrated in the 2~4 nm range, and TMP is enriched in the 0~2 nm near-interface layer, with their distribution characteristics determined by molecular structures and interfacial interactions. Diffusion analysis reveals that the increase in grafting densities facilitates the diffusion of TDI and exerts a certain inhibitory effect on that of TEA, while no significant variation is observed in the diffusion of TMP; the diffusion capacity of TDI and TEA is enhanced with the elevation of temperature, whereas that of TMP shows no obvious changes. The radius of gyration (R_g) of PBT chains presents a variation trend of increase-stabilization-steep rise with the increase in grafting densities, and exhibits a nonlinear characteristic of initial increase, subsequent decrease and re-increase with the change of temperature. In addition, bulk phase model analysis indicates that the number of hydrogen bonds is closely correlated with the glass transition temperature and exerts a remarkable influence on the mechanical properties of the system. Moreover, the influence mechanisms governing the microstructure of the composite system are further clarified from the perspectives of hydrogen bond formation and interaction energy.