Abstract: Resources description framework （RDF）query language has semantic information,but it’s inefficient when dealing with great deal of data. The relational database can store and query very large data efficiently,but its query language SQL does not have semantic information. In this paper an RDF query engine is implemented to convert the query on RDF to SQL,so that users can query relational database by RDF query language transparently and efficiently. By this engine,use can be made of RDF’s semantic information and the advantage of efficiency query of relational database. Based on this way,the data in distributed heterogeneous databases can be queried and integrated.