One of the most serious limitations of traditional workflow management systems is lack of flexibility. This paper considers one of the main factors causing poor flexibility is the imperative nature of process management, which forms the foundation of traditional workflow system. To combine the advantages from both the policy management and the process management, a prototype policy based workflow management system (PWfMS) is presented. A meta-model for PWfMS is developed to support the system design and implementation. An extension to Petri net, Variation Petri Net system (VPN), is proposed to support the modeling and the analysis for new approach.