Execution of workflow management systems in pervasive computing environments, especially the multiple modalities of interaction between users and systems, has become an increasing requirement in many enterprises. Group activity is another salient feature of the business processes. Traditional workflow management systems have difficulties in supporting such features. Through extending traditional workflow model in modeling method and executing mechanism, we designed and implemented a group-supported workflow management system with the ability of interacting with users in multiple modalities. Compared with traditional workflow modeling method, this method has more capabilities in describing group activities and makes modeling simpler. This paper introduces the modeling method for group activity and the mechanism supporting interaction between users and systems with multiple modalities. The applications of the system in some enterprises are also introduced.