Security and flexibility are two important issues in workflow management systems. The RBAC flexible workflow model is proposed recently which captures above needs, however there exist an open issue of its role hierarchies. With the numbers of users and roles increasing, how to reduce down the complexity of management is emerging concernful. A novel method of role management is presented in this paper that introduce the notation of partial inheritance into the role hierarchies. Compared with other dominating methods, it can efficiently achieve the objectives of role management in flexible workflow.