By introducing "best practices" as standard process models, business process standardization and reengineering have assisted in achieving the efficiency of the project development. However, they have also resulted in many problems because a standard model has limited flexibility to suit different practices of different projects. This paper presents a Task-Based Modeling method (TBM) for modeling processes in project management. Key business tasks are defined as the basic task components. Supplementing each task with an execution method and detailed attributes, its action can be fully defined and its outcome can be measured. A business process model can then be created to meet the need of the particular business by using the task components as the basic building blocks. A request-driven approach is also proposed to instantiate an instance of a process model. A purchasing process is used as an example to illustrate the presented methodology.