Series of polyimide membranes with different thicknesses have been prepared using pyromellitic dianhydride and 4,4'-diaminodiphenylether monomers, and the properties of polyimide membranes have been measured by experimental techniques. The dynamic sorption and steady permeation behaviors of water, methanol, ethanol, and dichloromethane as well as the steady permeation of the methanol/dichloromethane binary system in polyimide membranes were investigated. The experimental results show that the diffusion of water in polyimide membranes is more rapid than those of other penetrants in this study, and the diffusion behavior of water exhibits the typical characteristics of Fickian diffusion. However, the sorption curves of methanol, ethanol, and dichloromethane are typical of a sigmoid shape, and there are no evident linear relationships between the flux and the reciprocal of membrane thickness. This is in conflict with the Fickian law, and it can be concluded that the diffusion behaviors of methanol, ethanol, and dichloromethane in polyimide membranes under the experimental conditions belong to the anomalous diffusion.