Awareness of the need for process orientation in IT support field has been increasing these decades, which made the modeling and analyzing of business process become more and more significant. Among various formal methods, Petri nets were applied in workflow management, mainly because its visible feature based on the rigors graph theory. As another potential candidate, Pi calculus, a branch of process algebra, proved to be more capable in modeling mobility and interaction. But there were no formal methods to integrate these two formal methods, even this work may be of great significance. In this paper, based on the analysis of both Petri nets and Pi calculus, we will introduce a mapping model between those two formal methods, which integrates the workflow model of Petri nets and the interaction model of Pi calculus to describe collaboration business processes.