Gas/vapor permeation has become a common method for VOC (volatile organic compound) recovery and CO2 capture. The spiral-wound membrane module, which has high packing density, has been commonly used in gas/vapor permeation. In this study, the model that suits the spiral-wound PDMS (polydimethylsiloxane) membrane is obtained by using an integral transform from an N-S equation (Navier-Stokes) and a mass transfer differential equation. The predicted results indicate that the concentration polarization and spiral-wound membrane structure influence can be neglected. The mass transfer based on the MS-UNIQUAC (MS-U) model is also proposed and compared to that based on the Fick-Henry (F-H) model. The comparison results show that the mass transfer based on the F-H model can only be used in a gas mixture without condensable gas; the MS-U model should be used for a gas mixture that includes condensable gas. The influence of permeate flux and feed-side composition in the spiral-wound membrane at different operation conditions is also investigated using the MS-U model. (C) 2012 Elsevier Ltd. All rights reserved.