With the rapid growing popularity of XML to represent data, how to make good use of XML data in relational databases is worthy of study. Storing XML data as text in relational databases is a traditional strategy which cannot reflect the feature of XML format. In this paper, a mechanism for XML data storage and query in relational databases is proposed. XML data can be stored in relational tables and XQuery expressions can be evaluated as a part of SQL for XML data query. XQuery grammar tree and Query tree model for XML data query in rela-tional databases is presented to gain more efficient performance while querying XML data. Appropriative algorithm for evaluating XPath is also presented in this paper by which XQuery can be evaluated rapidly and efficiency. Finally, experiments invalidate the strategy of XML storage and run the algorithm on real XML datasets to show the efficiency compared with other mechanisms.