Supporting dynamic changes and flexibility is required when workflow management systems are employed. Related research work are all focused on some special changing issues. A process meta-model is proposed to guide the design of workflow process model. The process meta-model supports dynamic changes of workflow process. Its dynamic characteristics of workflow process from the points of view of time and process levels are surveyed, and the workflow meta model proposed by workflow management coalition is extended. This process meta-model enables the dynamic characteristics to be described in build-time and enables the changes of a process to be handled with these pre-defined characteristics. Based on this meta-model, a workflow management system possesses the flexibility without losing the control of workflow process.