During the recent years, Service-Oriented Computing (SOC), as a new computing paradigm, has been widely accepted in academies and industry. More and more service-oriented computer system analysis and design methodologies have been proposed. It is believed that if a service-oriented methodology is based on compatible concepts and description methods between the application domain and the system responsibility, it would take more advantages. So, in this paper, a Unified Service Description Language (USDL) is suggested based on our understanding of service and its attributes to unify description of web service and general service in application domain. With a demo in DELCCA project, USDL is asserted to efficiently support service oriented analysis and design.