To comprehensively evaluate the thermal safety of energetic plasticizer/binder composite systems， a multiscale thermal analysis strategy was applied to N-butyl-N-（2-nitroxyethyl）nitramine （BuNENA）， poly（3，3-bis（azidomethyl）oxetane-co-tetrahydrofuran） （PBT）， and a BuNENA/PBT composite system with a mass ratio of 1∶1. Differential scanning calorimetry （DSC）， non-isothermal kinetic analysis， slow cook-off tests， 5 s explosion point tests， and self-accelerating decomposition temperature （T_SADT） calculations based on the Semenov model were used to investigate their thermal decomposition behavior and thermal safety characteristics. The DSC results showed that BuNENA mainly underwent exothermic decomposition at 180-240 ℃， whereas PBT decomposed in a higher temperature range of 220-300 ℃. The BuNENA/PBT composite exhibited two exothermic peaks， and the first exothermic peak shifted to a higher temperature with a reduced low-temperature exothermic intensity， indicating that PBT could suppress the concentrated heat release of BuNENA at relatively low temperatures. Kinetic analysis further showed that the apparent activation energy of the first decomposition stage of BuNENA/PBT increased compared with that of pure BuNENA， suggesting an enhanced thermal decomposition barrier. In the slow cook-off test， the initial reaction temperature increased from 151.6 ℃ for BuNENA to 162.5 ℃ for BuNENA/PBT. The 5 s explosion point increased from 261.5 ℃ to 290.2 ℃. For a 25 kg package， the no-return temperature （T_NR） and SADT of BuNENA/PBT were 134.7 ℃ and 128.1 ℃， respectively， which were higher than those of BuNENA. These results indicate that compounding BuNENA with PBT can reduce low-temperature concentrated exothermicity and improve the thermal safety margin of BuNENA-based energetic composite systems under slow heating， transient thermal stimulation， and storage-related thermal conditions.