Design studies on the superconducting helical coil of Heliotron G reactor are reported. Neither demountable nor modular helical coil system was adopted. The continuous helical coil with the cryostat is constructed in a body with a plasma vacuum vessel. Three design examples will be described. For pool boiling and forced flow cooled types, single-layered coil is proposed so as to ensure the reliability of the insulation and of the helical winding. Large current conductors are designed. For superfluid bath cooled type, a conductor available in the present stage is used and multi-layered coil is designed.