Workflow is playing more and more important roles in more and more domains. But there are still no effective solutions to workflow modelling for huge systems. In this paper, conceptual modelling engineering is introduced into work flow modelling to extend the modelling process. The whole workflow mode lling process is then divided into four phases according to modelling engineering. Formatted description and formal description are particular expatiate d in this paper. Conceptual ontology is very import for formatted deseription.