The blend of nitrocellulose (NC) and polyethlene glycol (PEG) was prepared by solution blending method. The interaction between the two components PEG and NC, and the microscopic structure of the blend were characterized via infrared spectroscopy and polarizing microscope. Results show that there is a strong interaction between NC and PEG, and PEG fragmentary crystallites disperse in the blended system. The mechanism of the interaction between NC and PEG was studied by molecular dynamics simulation, and the microscopic structure and density distribution were obtained by the mesoscopic dynamic simulation. The above two simulations have a good accordance with the experimental results. Molecular interaction and microstructure of NC/PEG system can be characterized by molecular dynamics and mesoscopic dynamic simulation.