Abstract: Existing design methods could not give enough support to the design process of distributed systems which involves mobile computing. Proposed in this paper is a new ADL （architecture description language） that could be applied to distributed systems including mobile agent systems, LXL. LXL takes join-calculus as its formal basis. Since join-calculus has more intension to be designed as a core programming language, a cross-cut is made on join so that it is more suitable to be a specific language. LXL is significantly different from the existing ADLs by introducing the construct of container. A container is defined as a logic location, and also can be regarded as an agent, since a location is defined as a group of running processes residing on a physical site. Thus the concept of a location and a component is unified. With these facilities LXL provides mobile application system design and analysis with enough support.