Abstract: For most real-time operating systems, only the event-triggered mechanism is supported. This paper proposes a scheduling mechanism which can support not only time-triggered but also event-triggered tasks in μC/OS-Ⅱ. For safety critical tasks in this embedded system, a simple and easy scheduling algorithm is also presented based on criticality degree based priority (CDBP). This algorithm ensures the execution of the emergency tasks at a low level and the execution of the higher critical tasks at the high level while reducing the unnecessary task switching overhead. Experimental results show that the proposed algorithm is better than own criticality based priority (OCBP) algorithm in improving the system efficiency and provides better support for the criticality tasks and emergency tasks.