<p>Nitrate ester plasticized polyether (NEPE) propellant exhibits high energy and favourable mechanical properties, rendering it a promising choice for propulsion systems. Nonetheless, the lack of comprehensive microscale pyrolysis mechanism investigations has hindered its further advancement. During the thermal decomposition process, NEPE releases various small groups, including NO, NO₂, OH, NH₂ and HCN. Studies indicate that these small groups play a significant role in promoting pyrolysis. Therefore, this study employs quantum chemistry to explore the promoting mechanism of key components in NEPE propellant by small groups. Specifically, the promotion mechanisms of the oxidant HMX and the binder PEG/NG/BTTN by small groups are calculated and analysed. Initially, the adsorption mechanism for each promotion mechanism is determined through electrostatic potential analysis, followed by the calculation of reaction paths and energy barriers. The results reveal that the energy barriers for the pyrolysis of HMX/PEG/NG/BTTN promoted by small groups are notably lower compared to direct pyrolysis. Particularly, the energy barriers for the pyrolysis of HMX/PEG/NG/BTTN (87.5, 22.7, 120.0, 249.0 kJ·mol⁻¹) promoted by the OH radical are significantly lower than those for direct pyrolysis (200.6, 305.3, 146.1, 278.4 kJ·mol⁻¹). The pyrolysis of NEPE key components is substantially enhanced by small groups, particularly the OH radical. This research contributes valuable theoretical insights for regulating the pyrolysis behaviour of NEPE propellants.</p>