Abstract: Exception handling is one of the key issues that computer supported cooperative system must encounter Properly describing the procedure of exception handling is helpful to designing and implementing the funetions in a workflow management system Petri net is a appropriate tool for validating the correctness of process definition and giving evaluation But it is burdensome to describe a variety of procedures under different conditions In this paper, the handling elements including activities, exception events, strategies, and methods are described by means of an intuitional formal presentation, and especially the handling procedures are described under different strategies With message based mechanism, the temporary information produced by the interrupted activity instance is first analyzed and then how to process information by formal presentation is described Finally, the relationship in compensatory operations between exception handling and transaction processing is illustrated The formal presentation of exception handling is the groundwork of coding and implementing exception handling in WfMS