The invention relates to an index file. The index file comprises an index word module for storing an index word, a frequency module for storing the occurrence frequency of the index word, a word source file module for storing the information of all words in the file in which the index word is and a file information module for storing the file information which contains the index word, wherein the index word module comprises index word information and a word frequency pointer which is linked to the frequency module according to the index word information; the frequency module comprises the number of the file in which the index word is in the file information module, and the occurrence frequency of the index word in the file in which the index word is; the word source file module comprises the information of the index word in the word source file, and a storage position pointer linked to the frequency module; the file information module comprises the file information which contains the index word, and a file pointer linked to the word source file; the index word module is linked to the frequency module through the word frequency pointer; the file information module is linked to the word source file module through the file pointer; and the word source file module is linked to the frequency module through the pointer storing position pointer information.