Abstract: With the theory of space engagement, the necessity and feasibility of the modification of enveloped toroidal worm-gearing are analyzed and demonstrated. The essentiality and law of the modification are discovered. Accoding to the modification theory, the basic type of the modification of toroidal worm-gearing –– curvity modification is put forward, from that the maths expressions and calculate formulae of the curvity modification are derived.

Key words: Curvity modification, Toroidal worm