Abstract: Product assembly design is a complex design activity which may involve collaboration among designers geographically distributed. And the development of virtual reality applications for assembly design can provide designers with a more realistic environment to evaluate their assembly process. We create a web-based virtual environment supporting designers from different places with different platforms to engage in the same assembly scenario and complete the assembly task synchronously. This paper firstly presents the architecture of the environment based on an assembly design scenario. Secondly, two key technologies including multimodal interaction and task processing, which are closely related to the architecture, are discussed in detail. At last, we give our implementations and discuss limitations in our current research effort.