1. A method for establishing relationship between documents in term of a user's operation upon a document search result, wherein the document search result is obtained from a search based on one or more search queries, the method comprising: monitoring the user's operation upon the document search result; obtaining one or more documents selected by the user according to the operation and storing a related document list for the selected documents, the related document list being different from the document search result; depicting a document relationship according to the related document list by using at least the one or more search queries, and creating a document relationship table stored in a document relationship repository, the table containing a relevance degree of the document relationship between at least one pair of the documents in the search result, wherein at least one of the selected documents is opened by the user for browsing, in the search result, and the relevance degree between said pair of documents is a query-based relevance degree averaged over at least two search queries; and wherein said at least one of the selected documents meets a criteria for being a related document, the criteria comprises one or more following conditions: whether the duration of the selected document being opened exceeds a predefined period; the number of times of the selected document being opened exceeds a predefined value; the selected document is opened within a predefined time frame; and the selected document is opened in a predefined opening sequence.