Abstract: By expanding the surface currents on the helix tape in a series of chebyshev polynomials, simulating the helical thickness with vacuum layer, equaling the rods with multiple azimuthally symmetric layers and considering the loaded-vanes, the dispersion equation, interaction impedance and attenuation constant of helical slow wave structure with arbitrary tape width,supported by a radially stratified dielectric layer which is adjacent to the loaded vanes and enclosed by a metallic shell are obtained. The calculating results show good agreement with the experiment results. The theory can provide a strong basis for design of the helical s1ow wave structure.