A mathematic model is developed for the perovskite-type mixed ionic-electronic conducting (MIEC) membrane, which makes it possible to simulate the process of oxygen separation in the U-shaped Ba0.5Sr0.5Co0.8Fe0.2O3 (-) (delta) hollow-fiber membrane. The model correlates the oxygen permeation flux to the measurable variables. The trends of calculated results for purge operation coincide well with the experimental data, therefore the model is considerable for flux prediction under vacuum operation. Higher oxygen separation efficiency can be achieved with vacuum operation than purge operation. Parameter study with vacuum operation reveals that oxygen permeation flux increases with higher vacuum levels, and vacuum pressure of around 1.013 x 10(3) Pa is the optimal. Also, vacuum operation on the lumen side is much more efficient to achieve higher oxygen permeation flux compared with compression mode on the shell side. (C) 2017 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.