To investigate the diffusion behavior of hydrazine hydrate in nitrocellulose （NC）–based propellant and its influence on the gradient distribution of nitrate ester groups on the propellant surface， molecular dynamics （MD） simulation combined with experimental characterization was employed to study the diffusion process during the construction of a nitro gradiently distributed propellant （NGDP）. An NC/N₂H₄/H₂O ternary system was established to examine the effects of NC nitrogen content， reaction temperature， and hydrazine hydrate concentration on diffusion behavior. Meanwhile， NGDP samples were prepared through a one-step green synthesis route， and their structural and compositional distributions were characterized using extended-depth-of-field microscopy， Raman line-scanning， and X-ray photoelectron spectroscopy （XPS）. The results show that an increase in the NC nitrogen content significantly enhances the diffusion coefficient and free-volume fraction， and increases the radial distribution function （RDF） peak intensity， indicating that higher nitrogen content facilitates hydrazine migration and strengthens local interactions. Higher temperature and hydrazine concentration also promote diffusion and enlarge the free-volume fraction， while decrease the RDF peak intensity， reflecting a more dispersed local configurations under intensified molecular motion and weakened short-range interactions. The thickness of the reaction layer increases with increasing temperature and concentration， and both the characteristic peaks of nitrate ester groups and the N 1s content gradually increase from the exterior toward the interior， exhibiting a graded distribution.