Abstract: A new method of liquid impregnation combining air oxidition is employe d to modify the surface and pore structure of PANbased activated carbon (PAN ACF) under moderate condition.By this method,a molecular sieve type PANACF is prepared having high selectivity to separate N2 from O2.TGADGA,electronic bala nce and XPS are used to characterize the performance and surface chemistry of th e samples.The results show that PANACF impregnated with condensed coal tar has a slight weight loss during 100～400 ℃,the benzenoid and heterocyclic compound graft with carbon fiber by the aid of oxygen molecule to tailor the pore and su rface structure of fibers.After oxidizing by air,the selectivity and adsorptive capacity of PANACF are improved significantly,the selectivity reaches 5.6 of N 2/O2.There are many kinds of function group such as hydroxyl group,ether,carbony l and carboxyl after the impregnation of PANACF with condensed coal tar and ox idized by air,during oxidition the content of various function group changes,gra phitelike carbon increases with the increase of impregnated concentration.