Abstract: A transport model of penetrants in glassy polymer membranes has been established. The sigmoid sorption curves and corresponding desorption curves can be satisfactorily simulated with this model and can be extended to the Fickian and case II diffusion. Based on this model, a method for evaluating diffusion coefficient concentration relation from experimental sorption and/or desorption curves is suggested. Both the correlated and predicted results agree well with experimental sorption and desorption curves of alcohol in polyimide membrane. It is shown that our model is simple in form and higher in precision comprising with Crank's model.