Task scheduling is an important research topic of real-time systems. Compared with the common real-time systems, CNC system has its own features. In this paper, we propose an adaptive task scheduling model for CNC system and analyze its schedulability. The model is suitable to the uncertainty of open computing environment and can accept the running of different types of tasks. It can compute band changes according to the latest changes of system resources and task requirements. It adjusts tasks’ priorities adaptively and makes the system run in optimal real-time performance. On the basis of CNC system, we will further optimize the model by studying the characteristics of periodic tasks and scheduling time overhead. Finally, this model will be used in practical CNC system.