Abstract: With the rapid development of network technology and the arrival of information period, information sharing has become a more and more important issue today in all enterprises. However, the structural heterogeneity and the geographical distribution of information make this problem more difficult and complex. In addition, the efficiency of query information from the Internet is too poor to satisfy the requirement. In this paper, a model of MUIS (multi-domain union of information sharing) is proposed to deal with this problem, which could be propitious to the information sharing and information retrieval across the multiple domains. The model can efficiently integrate and share heterogeneous databases geographically distributed and resided in different environments with the multi-agent cooperation. After summarizing the model of single-domain union of information sharing, the overall structure and major components of the model of MUIS, including standardization of heterogeneous databases, URI remote access, cross-domain query, inter-site query, and natural language interface are presented. The detailed definition of several kinds of agents and the multi-agent cooperation in this model are also presented. This system is implemented and applied in several areas such as agricultural information sharing and yellow pages sharing, and currently each MUIS system contains some databases from several websites.