Abstract: A mathematical model for evaluating the separation performances of hollow fiber membrane N2-H2 permeators has been established. The effects of operating parameters and membrane characteristics on the concentration of hydrogen in the permannte gas and the percentage recovery of hydrogen have been studied with the help of a digital computer using this mathematical model. Results computed are compared with data obtained from field tests of three φ100 × 3000mm full-scale permeators, confirming the adaptability of the mathematical model.