The study of the geometry for worm-gearing is much more complicated than that of plane gearing, since worm-gearing is three-dimensional. A numerical method to determine the conjugate profile of worm-gearing tooth is developed. The software, with numerical set-up and graphic display, is an original and special program, and it could be adopted for the geometry of any kind of cylindrical worm-gearings, as well as for spur gearings and bevel gearings.