The thermal interface resistance of the helix slow-wave structure （SWS） has been studied theoretically and experimentally. The effect of the thermal resistance at two interfaces on heat dissipation capability of the SWS is analyzed. A novel method to calculate the thermal interface resistance has been developed, and its accuracy and feasibility were validated by experiments. With this method, the thermal interface resistances at two interfaces can be calculated separately, considering the variation of the material performance with the temperature changes. This novel method is used to study the effect of the rod material and the assembling method on the thermal interface resistance.