In order to investigate the barrier properties of multi-layer moisture-proof composite plastic films against water vapor molecules， the diffusion and adsorption behavior of water vapor molecules in the composite films were studied by molecular dynamics simulation. And the permeability coefficient （the product of diffusion coefficient and solubility coefficient） of water vapor molecules in the composite films were obtained by using the parallel model. The results show that the diffusion coefficient of water vapor molecules in the composite films increase with the increase of temperature， while the solubility coefficient gradually decreases with the increase of temperature， and the permeability coefficient gradually increase with the increase of temperature. At the same time， polyvinylidene chloride（PVDC）exhibits the best water vapor barrier performance in the moisture-proof membranes， followed by polyethylene（PE）， and finally nylon 6（PA6）. Additionally， to study the aging resistance of the composite films， the chemical structure and thermal stability of the composite films under different aging times and relative humidities were studied by Fourier infrared spectroscopy， thermogravimetric analysis and differential scanning calorimetry. The results show that composite films exhibit excellent stability， with no significant changes in material properties.