Process performance of a multi-bed pressure swing adsorption(PSA) process to simulate a countercurrent flow of adsorbent for separation of a binary gas mixture was analyzed theoretically. A multi-bed PSA cycle was simplified to an one-bed cycle in order to reduce difficulties in simulation. Material balances were formulated in gas and adsorbent phases under the assumption of linear isotherms for components and isothermal operation. The mass transfer within an adsorbent was described by linear driving force model. The system considered in this study was nitrogen production from air by carbon molecular sieve. Process performance was examined in view of productivity and recovery, and was related to the fraction of bed utilization for oxygen. The effect of complete and incomplete regeneration during a purge step on performance was investigated respectively. Process performance increases or decreases as the number of bed increases depending on the operating conditions and has a close relation with a fraction of bed utilization for oxygen.