In analysing the capability of the heat dissipation of the helical slow wave structure elastically （or expansively） supported by round dielectric rods

two difficulties are encountered: one is how to calculate the contact area and the other is how to determine the interface thermal resistance. So far only very few papers have dealt with this subject.An attempt is made to solve these two difficulties in this paper. A model is constructed. The formula related to the distorted force with the interference is derived. The contact area between the rods and the helix （or the barrel） can be calculated using the analytic results of elastic mechanics. As a result of the analysis

it is believed that the interface thermal resis tance is actually caused by the reduction of the effective contact area due to a bad contact. Therefore it can be taken into consideration by introducing an area correction factor.Various factors

such as the geometric size

the physical properties of the materials

the interference and the expansive correction

are taken into account in the computer programming and a lot of calculations have been done.The theoretical calculation is in close agreement to the experimental results. Some useful data for the practical design of heat dissipation are obtained.