Real-time　scheduling　is　a　key　in　real-time　system,　and　real-time　dynamic　scheduling　is　the　main　part　in　real-time　scheduling.　When　carry　out　theoretic　analysis　of　real-time　scheduling,　real-time　theory　assume　that　system　owns　enough　number　of　priority　levels.　But　in　practical　tasks,　system　only　limited　priority　levels　could　be　used.　In　practical　tasks　system,　analysis　for　dynamic　scheduling　included　two　continuous　parts:　judged　method　that　tasks　systems　require　minimum　number　of　priority　levels　for　dynamic　scheduling　and　grouping　algorithm　for　tasks　system.　On　the　basis　of　previous　result,　the　paper　presented　grouping　algorithm　for　tasks　system　and　judged　condition　for　best　grouping.　The　steps　and　the　process　for　the　algorithm　are　described　in　detail.