On the basis of solution-diffusion mechanism and incorporation of a pseudophase-change phenomenon, the pseudophase-change solution-diffusion (PPCSD) model is developed for pervaporation of a binary mixture through a membrane system. Flux equations of individual components thus derived clearly describe the role of coupling flux in pervaporation and show that it depends mainly on the solubility and mobility of the other component in the membrane. Good agreement is found between the theoretical and experimental results (from literature values for the hexane-heptane-polyethylene system). In addition to the solubility and mobility of individual component, the pervaporation performance of a membrane is influenced by the effect of plasticization and coupling flux, especially when strong interaction, occur between the permeants and the membrane. A parameter study indicates that both plasticizing and coupling effects enhance the permeation rate and usually lead to a decrease in membrane permselectivity.