Abstract: Abstract: The preparation methods of carbon membranes, their key factors, as well as their separation performance compared with those of polypyrrolone and polyaniline membranes, are summarized. The future research direction is proposed. It is pointed out that carbon membranes possess excellent performance for oxygen and nitrogen separation with the oxygen/nitrogen separation factor of above 10, and a maximum value as high as 36. The polyimide- and polypyrrolone-based carbon membranes show better comprehensive performance for oxygen and nitrogen separation. The performance of these membranes breaks through the Robeson upper boundary, making them commercially attractive. Carbon membranes show great potential for commercial application for directly separating oxygen over nitrogen from air.