The invention discloses a Web data mining system based on XML. The system comprises a user interface module, a preprocessing module, a data mining module and a result accessing module. The problem of Web data mining is solved effectively, by XML, structural data from difference sources are effectively combined, searching in diversified difficultly compatible databases is possible, and the technical problem of Web data mining is solved effectively. In addition, owing to powerful expansibility and flexibility of XML, XML is allowed to reasonably describe various application software data, the gathered Web data records are convenient to describe, and therefore, favorable conditions are provided for software developers and Web terminal and station users.