In model-driven approaches, user interface description languages (UIDL) often existed as the model and played an important role in the user interface development process. With the increase of the scale of software and the appearance novel devices and interaction techniques, user interface have changed greatly. Former UIDLs did not perform well in the support of new interaction paradigm. Because of this, the study proposes an extensible UIDL: E-UIDL. This UIDL follows several roles such as hierarchy and modularity. It can support the description of pen based user interfaces and multi-device user interfaces. This paper describes the features of E-UIDL in depth.