Abstract: A permanent magnet frame based on ‘magnetic sieve’ effect for oxygen enrichment from air was theoretically studied.In the magnetic field space formed by two square permanent magnets,the central magnetic flux density and the capability of intercepting oxygen molecules increase with the thickness of magnets increasing,but the increase speed slows down.The enhancement of magnetic flux density by increasing the thickness of magnets is not infinite.For the specified thickness and length of magnets,the magnetic flux density and magnetic uniformity across width in the magnetic field space decrease with the width of magnets increasing.The magnetic uniformity required by the characteristic of the ‘magnetic sieve’ can be satisfied only when the thickness-to-width ratio of permanent magnets is larger than 1.For the given thickness and width of magnets,the magnetic flux density in the magnetic field space is less influenced by the change in length of magnets.Therefore,appropriately increasing the length of magnets can prolong the flow time of air and improve oxygen enrichment by the ‘magnetic sieve’.