Abstract: In this paper, the authors plotted out the basic units of workflow and analyzed their operational features. By making use of the delay among the processes of workflow and the reuse of manpower resource, a thinking of flexible Workflow was presented based on the product logical structure from the view point of concurrent engineering. According to this idea and knowledge of graph theory, a model of flexible Workflow based on the holographic tree structure was constructed to show the logical relationships in the process of product development. By this way the logical information and the process of Workflow were united organically. The authors also give the architecture of relational database supporting this flexible Workflow model.