As the applications of real-time systems are becoming more and more popular, the system scheduling mechanism faces new requirements and challenges because of the coexistence of different kinds of real-time and non-real-time tasks. The open real-time system has been paid attention because of giving a way to solve the problem and also brings new ideas to scheduling theory and approach. Firstly, the basic concepts and theories of open real-time system are described. And then, a hiberarchy model for scheduling objects is presented. It adapts to the scheduling environment of open real-time system. Several related scheduling approaches are compared in detail, and their functional features, the applying scope, and some of their common characters are pointed out. The result come out that it is feasible to integrate different kinds of approaches, and this would be a direction. In the integrated scheduling mechanism, the advantages of each approach can be kept, therefore, the application requirements of open real-time system can be met better.