Abstract: Traditional workflow technology can't meet the requirements of real-time system because of the particularity of business with temporal factor. Thence the real-time workflow is defined for real-time system in this paper, and the metamodel of real-time workflow is established, expending the metamodel of traditional workflow to support the time constraint and exception in real-time workflow. The extended attributes include the start time and duration in activity model, the duration in workflow process, the concurrent constraint in concurrent activities etc. Besides, the timeout exception of execution of activities is considered, and the relationships between the application programs and activities executed by them are established in the metamodel. Based on the metamodel, a UML based real-time workflow description language is defined by using profile mechanism, which is extended from UML2.0. The modeling principles are discussed to describe a real-time workflow by using this language firstly; and then the UML based extension technology and the profiles of the language are introduced; finally, a specific example of shipborne combat system is given to explain the modeling approach. This work provides a language which is easy to learn, use and understand for workflow designers, and basis for the execution and time analysis of real-time workflow.