In this paper we introduce a weighted XML data model based on traditional XML data model. We can use this model with the same DTD structure to express many common applications such as personalized ontology. Subsequently this paper discusses the weight value assignment methods in two situations which include comparison of XML data instants based on same DTD and expression of weighted XML data model in personalized ontology. And we design a new similarity algorithm of this weighted XML data model. At last, some experimental implementation and results are discussed.