The confined mass transfer separation membrane is mainly for the high-precision separation process at the molecular/ion level, which is of great significance to solve the application needs of CO2 separation, azeotrope separation, lithium extraction from salt lake, desalination of seawater and so on. However, at present, the research of the confined mass transfer mechanism of this kind of membrane is lagging behind, and the theoretical models of confined mass transfer are lacking, which can no longer meet the needs of the rapid development of materials and chemical engineering. From the perspective of meso-science, the abnormal phenomenon of high flux and high selectivity of the confined mass transfer separation membrane is considered, that is, breaking through the trade-off effect, which is governed by compromise-in-competition between the selectivity mechanism and the flux mechanism. It is found that the fluid molecules will preferentially adsorb at the interface and form a stable adsorption layer. Based on this, the hypothesis of "secondary confinement" is put forward, that is, the surface induced new solid-like interface will have confinement effect on the intermediate fluid again. By comparing the pore size and the secondary confined size of the confined mass transfer separation membrane, the selective mechanism of the secondary confinement is further confirmed, and the quantitative prediction of the membrane flux and selectivity is preliminarily explored by combining the selective mechanism and the flux model, which may provide a theoretical basis for the precise construction of the limited area mass transfer membrane. © 2020, Chemical Industry Press Co., Ltd. All right reserved.