The diffusion coefficients and mechanisms of NG(nitroglycerin), BTTN(1,2,4-butanetriol trinitrate) and TMETN(trimethylolethane trinitrate) in PEG/N-100(polyethylene glycol/curing agent) were studied by molecular simulations. The order of diffusion coefficients is NG > BTTN > TMETN. By comparing the three systems, the weakest diffusion of TMETN was attributed to the following two aspects: firstly, the strongest binding force between TMETN and PEG/N-100 as well as the weakest self aggregation ability of PEG/N-100 in the system; secondly, the largest size of TMETN among the three plasicizer systems. The effects of temperature and plasticization ratio on the diffusion properties of TMETN were investigated. With the increasing temperature, the diffusion coefficient of TMETN increased slowly at first and then sharply, which was consistent with the law of accelerated aging at high temperature; the position of hydrogen bond moved backward and the peak value decreased owing to the high temperature, suggesting the weakened interaction between plasticizer and binder; meanwhile, the fractional free volume of system increased. With the increase of plasticization ratio (2.5, 2.8, 3), the diffusion coefficient of TMETN decreased. Mesoscopic studies showed that the improvement of compatibility was one of the reasons.