In view of the fact that communication and interaction are major factors to the success of a simulation project, this paper presents an integrated architecture with group communication and model design which is implemented to form a collaborative Web-based DEVS (Discrete Event System Specification) simulation environment over the Internet. Our system shows a paradigm-shifting activity to differ from the so-called one-person-alone Web-based simulation. During the entire modeling process the system will utilize an XML document and present its corresponding DEVS digraph-model applet and model code frame so that users in different places could view the same model and exchange their opinions and comments at the same time thus producing better result. This paper also demonstrates our implementation with a modeling example to illustrate how group interaction is to facilitate and improve the Web-based model design.