The development of E commerce is booming. Now the management of some domain is converting from tradition to E commerce, this needs the application and integration of the latest information technologies for the maximum usage and share of network information resources. As a modeling language, Unified Modeling Language (UML) is well defined, easy to specify, powerful in function and applied widely. Business model concentrates on the business around the system, not every project requires business model. However, there are many situations where business modeling adds a great deal of value. Establishing system business model is the primary task when people make use of UML to establish E commerce system model and develop software system. By E commerce system the authors expound the use case, and propose how to use correct method to establishing E commerce system business model.