This paper discusses the issue of information interoperability. In view of the problems that it is difficult to solve the semantic conflicts in information interoperability, the paper shows how to build the extension ontology model for information interoperability based on Extenics information-knowledge-Strategy system. Take advantage of Extenics' feature of contradiction problem solving, the extension system can eliminate semantic conflicts by extension transformation method. It overcomes the drawbacks of current ontology models that lacks transformation mechanisms, therefore supports information interoperability effectively. The paper presents examples of semantic interoperability process with the extension system. It describes some implement technologies of the extension system.