Abstract: 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.