Personalized support for users becomes even more important, when service access takes place in open and dynamic service-oriented environment. This paper shows how to realize personalized service support in cross-system/service environments based on ontology and Web service technologies. First, we introduce the related approaches for supporting cross-system personalization and give their insufficiency respectively. Aimed at the problems we propose a Web service based architecture for cross-system personalization. The loosely coupled structure of Web service can easily integrate personalization service from various information systems and provide seamless access to the users. In order to reuse user models we also present an ontology based user model to support cross-system personalization. Compared with the existing approaches, our approach can effectively support the various existing personalized systems and user models, and the realization of cross-system personalization is more simply and efficiently.