Abstract: To improve the flexibility of workflow management systems and solve problems in dynamic changes of workflow instances,a new method based on Petri-net is proposed.This method can automatically achieve dynamic changes of workflow instances caused by runtime adjustment of workflow templates and avoid abnormal termination of workflow instances at the same time.In this method,routing relations between workflow nodes are expressed by routing matrix and the current state of each place in the workflow instance are expressed by state matrix.Both matrices are employed to monitor dynamic changes of node relations and place states in the workflow instance.An immediate change algorithm to find bypassable nodes and migration nodes in time of workflow template adjustment is proposed.Migration strategy of each workflow instance is determined by bypassable nodes and migration nodes found.Finally,an engineering change process is given as an example to verify the feasibility of this method.