The agility of modeling business process simulation (BPS) is required by virtual enterprises. Firstly with some new concepts, such as the atomic business process simulation model (BPSM) and the business process simulation federation (BPSF) etc., a frame of business process simulation model for virtual enterprises (VE-BPSM) is presented. Business processes of a member enterprise are classified into three groups: internal, external and hybrid eventtriggered processes. The inter-relationship among them is discussed. To facilitate the business process simulation model for a member enterprise (MEBPSM) to be reused, every external-event-triggered BPSM or every hybrid event-triggered BPSM is built as an atomic business process simulation model (Atomic-BPSM). The VE-BPSM can be built as a BPSF through combining Atomic-BPSM of member enterprises, so the agility of modeling BPS for a virtual enterprise could be achieved. Finally, an HLA-based method of developing a VE-BPSM is discussed.