When making use of AutoLISP of AutoCAD to develop the CAD system of the worm hob, the functions provided by AutoLISP can''t fulfill all requirements in the design process of the worm hob. So some complementary functions such as calculating, dimensioning and drawing are developed to make an unattached module. It can be transferred by every module of the system. Through running the system, the necessity and the validity of the database are verified.