A design method and primary functions of pattern preparation system of computerized flat knitting machine are introduced. The system provides a formidable mapping system based on object-oriented and multi-document, so pattern becomes simple and flexible to be edited and displayed. In addition, the compiler has a novel method of compiling pattern data. Two pattern description files (PAT and CNT) are generated after compiled, which include all control information that computerized flat knitting machine needs. The system also provides a direct and friendly interface, through which user can accomplish pattern design quickly and conveniently.