While facing the challenge of e-commerce, the enterprises pay more attention to the business process re-engineering (BPR). A reasonable model to describe the business process is the key point to BPR sucess. Such a model should integrate all related business information and should be enacted by a system. Referencing on the WfMC (workflow management coalition) meta-model, a workflow model based on ECA rules and business activity decomposition is presented. The ECA rules imply the execution dependencies among the zctivities.Using rewriting techniques,the ECA(event-condition-action)model is transformed to Trigger-Action model to make the interpreation more efficient.Rewriting the event to the occurrence time of the event makes the event expression have more expressive semantics.Activity decomposition model can support the hierarchical project management.