Abstract: The surface equations of meshing gears and the curve equation of the meshing line are established. With several mathematic software and CAD software as assistance tool and using the theory of three-dimensional elastic bodies in non-Hertz rolling contact, the contact stresses at any point of the meshing line are analyzed and the effects of various meshing parameters on the contact strength are summarized. This supplies a new theory for the strength design of helical drive gears.