1. A system for generating derivative words, the system comprising: an input device used for inputting user character sets; a storage for storing a plurality of derivative grammar arrays, a plurality of derivative grammar arrays are stored in the storage, each derivative grammar rule array comprising a suffix alphabetic character set and a condition array corresponding to the base words, the condition array comprising a part of speech corresponding to that of the base word as required by the suffix alphabetic character set; a first match processing module, used for matching the user character set with each of derivative grammar rule arrays, and obtaining the derivative grammar arrays matching the character information; a second match processing module, used to obtain words from the language database in accordance with the user character set, the obtained words meeting the requirement of the condition array in one of the derivative grammar arrays as obtained in the first match processing module; a derivative processing module, used for adding suffix alphabetic character sets behind the obtained words to generate derivative words, the suffix alphabetic character sets being taken from the derivative grammar arrays having the condition arrays met by the words; and a language database, used for storing words; wherein the input device is a key input device, the inputting character information is a user key character set; and the second match processing module further comprises: a word searching processing module, used for obtaining words matching the user key character set inputted by the key input device from the language database; and a first comparing processing module, used for comparing the part of speech of each of the words obtained by the searching processing module with that of each of the derivative grammar arrays obtained by the first match processing module, and obtaining all of the words having the same part of speeches.