Abstract: A differential mathematical model for hollow fiber membrane gas separator including a gas pressure drop equation in hollow fibers was established and reduced to an algebraic one in order to simplify the calculations. The two models were tested experimentally and compared with the models in references. The models in this paper give better results than those in references when the pressure drop in hollow fiber can not be neglected. The models in this paper are very useful in design,calculation and development of hollow fiber membrane gas separator. The influences of inside diameter and length of hollow fiber and operating pressure on the separation process were studied. The optimum pressure of permeated gas in hydrogen and nitrogen separation process was about 0.4-1.0MPa.