To study the migration and diffusion phenomena of nitrates nitroglycerine(NG) and 1, 2, 4-butanetriol trinitrate (BTTN) as plasticizers in polyurethane elastomer under mesoscopic scale, the dissipative particle dynamics(DPD)simulation calculation was performed by molecular simulation software Materials Studio. A mesoscopic model of coarse graining was established. The diffusion coefficient of NG and BTTN in polyurethane elastomer was calculated by this model. Mesoscopic diffusion coefficient obtained by calculation is 1.80×10^-12 m²·s^-1 for NG, 0.21×10^-12 m²·s^-1 for BTTN, which is at the same level with microscopic results reported in literature, i.e. 0.65×10^-12-11.10×10^-12 m²·s^-1 for NG. After rising of molecular weight of prepolymer and temperature, the diffusion coefficients of nitrates increase. But the diffusion coefficient decreases with increasing the nitrate content. The diffusion coefficient of NG is bigger than that of BTTN under same conditions. The mesoscopic molecular simulation results agree with the reported values in literature and theoretical trend, indicating that the established coarse graining model of nitrate/ polyurethane can be used to investigate the diffusion case of the two nitrates in polyurethane.