Five kinds of polyimide membranes have been prepared using pyromellitic dianhydride (PMDA), 3,3'4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 4,4'-diaminodiphenylether (ODA), 4,4'-diaminodiphenylmethane (MDA), and phenylenediamine (PDA) monomers, and the properties of polyimide membranes have been measured by experimental techniques. The dynamic sorption and desorption behavior of water vapor in the five polyimide membranes at 298 K and 308 K were investigated by experiments. According to the results and the fractal diffusion theory proposed by Chen, the diffusion of water vapor in BTDA + PDA polyimide membrane belongs to anomalous diffusion, and the anomalous diffusion factors are 2.38 at 298 K and 2.26 at 308 K. However, the diffusion behavior of water vapor in PMDA + ODA, PMDA + MDA, BTDA + ODA, and BTDA + MDA polyimide membranes obeys the Fickian diffusion law. The diffusion coefficients for Fickian diffusion of water vapor in PMDA + ODA, PMDA + MDA, BTDA + ODA, and BTDA + MDA polyimide membranes were calculated from the dynamic sorption data, following Fickian diffusion. The values of the diffusion coefficient for water vapor in all four polyimide membranes at 308 K are higher than those at 298 K, and those at the same temperature increase,with the molar free volume of the polyimide membranes.