During web applications developed and deployed in many and many enterprises today, how to make sure their web applications satisfied to their individual and specific business requirements and marketing changes has been become a major problem. As now a lot of web applications are only designed and developed for specific business and they are normally high-coupled together with very bad system opening, collaboration, and flexibility. Here, by research on XML based web application design with software bus, component and workflow technologies, with multiple tiers layout and from user interface flexibility, business flow flexibility and data model flexibility, it illustrates a new way for a flexible web application design and try to improve web application flexibilities and to enhance enterprise satisfaction to their applications meeting with their business and marketing changes.