the present invention provides a semantic information acquisition method and system , and corresponding keyword expansion and search methods and systems , comprising : searching for , then classifying an article ; then , performing word segmentation according to the classified article to obtain the words in said category , and setting said category and words to serve as the semantic information of the keyword ; also , a method and system using the semantic information acquisition method to expand a keyword , and a method and system using keyword expansion to perform a search . the described semantic information acquisition method effectively avoids the technical problems in the prior art of only being able to obtain semantic information of english vocabulary ; and it also being impossible to classify semantic information based on category information . the invention is particularly suitable for searching using a keyword , searching a large number of texts , and organizing large amounts of related data and information .