Abstract: Centered on the two typical models of double-enveloping worm-gear drives in current gear industry,i. e.,orthogonal and non-orthogonal axes of worm and machine table for generating worm thread surfaces,a powerful computer program that can design and analyze the above two different models was developed. The program includes all state of the art technology,such as undercutting and contact boundary lines for both worm thread and gear tooth surface cuttings,relative curvatures,instant contact lines and contact stripes, meshing angles, relative sliding, tooth contact analysis( TCA), CMM measurement,single and double contact areas and their contact ratios,etc. The modern gear design method was illustrated by two numerical examples to design and analyze two different double-enveloping worm-gear drives.