Constructing an effective process module is groundwork for product development process optimization. This paper imposes an activity/process based modeling idea which supports the integrated management and optimization of process development process. This idea uses the activity/process as the modeling basic cell. At first, the activity/process based PDP modeling theory is studied; Second, the product Development process Modeling based on the Process/Action (DMP/A) method is forwarded. The basic elements and their properties are defined, then the steps of DMP/A are given in the paper. Through integrating the definition and description of process structure and activity/process attribute, input and output, the process model by DMP/A method helps to programmer, supervise and control the product development activities/processes, as well as communicate messages with each other. This provides a supporting tool for process development process integrated optimization.