A Dual Reflux PSA (DR-PSA) is a combined process of a conventional stripping reflux PSA and an enriching reflux PSA, and it has two refluxes and an intermediate feed inlet position. In this paper, a simplified mathematical model was developed to obtain a simple semi-algebraic Solution expressing the behavior of the DR-PSA process, and the effects of feed inlet position and reflux ratio off the process performance were investigated. The validity of the model was confirmed by comparing the model with existing experimental results. In addition, the model clearly described that the adsorbate concentration of the processed gas at the optimum feed inlet position is equal to that in the feed gas, and this fact has been experimentally confirmed. Also, the model Could be used to derive the optimum reflux ratio to achieve a required purification/enriching performance. The proposed model provides a simple design technique for the DR-PSA process, and it is useful for the optimization of the feed inlet position and the reflux ratio, which have considerable influence on the process.