In comparison to the industrial countries,our design principle and approach of wormgear hobs are not completed.There are no clear and accurate equations of worm-gear hob design,so do equations of machine settings of hob after re-sharpening.The basic principles of worm-gear hob design is presented,equations of hob size increase and machine settings of hob after re-sharpening based on the equations used in America gear industry are introduced,and finally,the error distribution between theoretical and hobbed tooth surfaces of worm-gears are analyzed.All provide the advanced technology of worm-gear hob design and manufacturing worm-gears for our gear industry.