Abstract: In complex and diversified application context, flexibility and scalability are one of the key issues of workflow technology. As an important approach with the ability of intelligible computing, semantic technology can be used to improve the capability of workflow. This paper defines a model of Meta-Object based on Petri-Net building block, and defines a workflow ontology named DAML-W based on DAML language. This paper also describes how to import semantic mechanisms to Meta-Object Protocol including protocol declaration, Meta-Object association and Meta-Object management. Furthermore, a methodology based on Multi-Agent system is proposed to implement the mechanism of semantic oriented workflow. Finally, a typical example demonstrates that the system based on semantic mechanisms combined with Multi-Agents could effectively improve the flexibility and scalability of workflow.