Abstract: This paper uses the tape helix model and considers the effects of dielectric, axially conducting shield and wire size on dispersion characteristics for the helix structure with longitudinally conducting vane. The actual dielectric rods are replaced by an equivalent dielectric circle. The formula of dispersion characteristics for this type of helix can be deduced from electromagnetic theory. A comparison with experimental data of references [3, 7] shows that they are very close.When the ratio between shield inner radius R and vane inner radius S is larger than 1.1 and the ratio betwenn vane inner radius S and helix mean radius a is smaller than 1.5, the difference between the theoretical value of the phase velocity and experimental values is within five percent. The general design curves have been calculated by computer. They can be used for the design and calculation of this type of helix structure in actual engineering practice.