A natural language dialogue system is composed of many parts: natural language process, dialogue management, data query, etc. Adding a new service function to traditional complex dialogue systems, which is based on a mixed initiative paradigm, for example Question Answering (QA) service for E-commerce website, requires in general a big effort for redesigning dialogue management modules and other important modules. The new architecture suggested in this paper is based on registration of Web services, and all the services are distributed on agents. It can balance between overall dialogue management and particular agent service. The new services to be added in the system need only register as agents with a central managing server. That makes application of complex QA system much easier for website service application compared to traditional architecture. We discuss the advantages brought by the new architecture, including more extensibility, more effective, platform insensitivity, wider adaptability etc., and describe in detail how to implement the system modules.