The shape and equation of tooth root fillet curve in the end face of helix gear by hobbing are studied.It is indicated that the circular arc of hob cutter’s tip has become elliptical arc surface in the end face of helix gear

so the tooth root fillet curve generated by hob cutter’s tip couldn’t be calculated with circular arc

otherwise to do so would influence the veracity of describing tooth root fillet curve

further would influence the correctness of results for a series of analysis and research works based on calculations above

e.g.the strength of tooth root

the interference of process

the design of hob cutter

the 3D forming

etc.The equation of elliptical arc of hob cutter’s tip in the end face of helix gear is mainly studied and analyzed

and the corresponding equation of tooth root fillet curve generated by the elliptical arc of hob cutter’s tip in the end face of helix gear is derived and built

and the research results above are applied to the soft for checking computations on processing gear

which written by author

and are verified.