The heat dissipation capability of the slow-wave structure (SWS) of the traveling-wave tube (TWT) is an important influencing factor that restricts the increase of the output power, the stability, and the reliability. Due to several unique and fascinating characteristics, the diamond material has been employed in the SWS manufacture to enhance the thermal conduction to a certain extent. The influences of the supporting rods deposited with diamond film, the helix deposited with diamond film, and the diamond supporting rods on the heat dissipation capability have been studied using theoretical, simulation, and experimental methods. This method is closely associated with the computer simulation in experimental test and increases the simulation accuracy. Valuable conclusions have been obtained.