In this paper we describe an analysis of the wave impedance and the attenuation constant of a shielded wire helix. Analyses are made by the wire theory. Helix analyses are chiefly done by the sheath theory and the tape theory, but these make models, that are infinitely thin ideal cylinders and infinitely thin tapes, so in the case where a helix wound with finite sectional area wires is used with shielding, conditions vary and it is insufficient for contributing to a design at the time when winding encounters difficulties: it is difficult to estimate the effect of the diameter of the wire on the attenuation constant α and wave impedance Z0. So the case in which the wire helix had a shielding cylinder was analyzed in this paper. The numerical results are also presented as graphs.