An enterprise is composed of different departments, and these departments work together to achieve goals of business processes collaboratively. However, most of these business processes comprise loose operations, and information can¡¦t be passed efficiently among them. Hence, if an enterprise wants to promote competence, the problem of inefficient execution of processes must be improved. And, if workflows could have more flexibility, it will bring more benefits for enterprises. In this study, there are four parts to discuss flexible workflows. Firstly, we discussed workflows including the definitions of flexible workflows. Secondly, we discussed resource management including workflows with resource management and constraints programming. Thirdly, we discussed project management including the definition of project management and techniques. Finally, we discussed medical flows including three kinds of medical flows. We propose a prototyping system architecture including workflow management, resource management and project management to implement flexible workflows. In the experiment, we use a medical flow to explain how this system works. And, this system can produce a feasible schedule by a constraint solver.