Patent data is one of the most valuable reservoir of technical and commercial knowledge. However, patent data of different countries and organizations has been stored separately, which added to the difficulty for patent analysis with these free patent data. By using Web mining method, we can retrieve the related patent information of a certain field from several patent Website as data source. From web pages to structural patent database, we can use these free patent sources to obtain professional patent analysis result and useful knowledge. A citation structure visualization method is introduced, which helps reveal the citation relationships among patents.