<p>During long-term storage of solid rocket engines, plasticizers will gradually migrate out of the propellant and enter the insulation layer. In order to analyze the deterioration of thermal insulation and flame resistance properties of the insulation layer, the thermal decomposition mechanism of NBR insulation containing the mixture of bis(2,2-dinitropropyl) formal/acetal (BDNPF/A) plasticizers is studied by combining ignition experiment and molecular dynamics method. Firstly, the density and thermal decomposition temperature of the molecular models are verified to be consistent with the experimental results. Then, through the X-ray micro-computed tomography (micro-CT) technology and morphological analysis of molecular models, it is determined that there is a phenomenon of phase separation between BDNPF/A and NBR components, and the gas decomposed in BDNPF/A component results in the formation of a porous structure in the insulation film. Finally, the molecular simulation results show that the primary thermal decomposition product of the nitrile butadiene rubber (NBR) insulation film containing BDNPF/A is nitrogen oxides, and the primary decomposition pathway is nitrous acid elimination (NAE). However, the decomposition pathway of NO₂ radical homolysis can only occur at low concentration of BDNPF/A and is more significant at high temperatures.</p>