As the membrane gas separation technology grows, various models were developed by many researchers to describe the separation process. In this work, the cross-flow model was compared thoroughly with other models, including the cocurrent model and counter-current model. Results showed that the difference between the cross-flow model and the other two models was quite limited for various models, especially for the low or medium purity product applications. Furthermore, the cross-flow model could be solved analytically and was simpler than other models. Therefore, the cross-flow model can be considered as a convenient model for gas separation process. To discuss the suitability, several typical processes of membrane gas separation were analyzed using different models.