Simplified and unsimplified (traditional) Chinese character conversion is very i mportant for the cultural and economic exchange between the mainland of China an d overseas Chinese speaking areas. In this paper, the design and implementation of an automatic conversion system is presented, which has been put into use. The system architecture is shown firstly, and some important data structures, the w ord dictionaries and mapping tables are presented. Then, the system processing f low is outlined, which includes preprocessing and post processing, ambiguity res olution, word conversion, etc. Finally, the system performance analysis and the test result are listed.