The invention discloses a slow wave structure used for an X-waveband space travelling wave tube. A tube shell adopts a Monel tube shell with the inner diameter of 1.9 millimeters, a holding rod is made of a wedge-shaped BeO99 material, the slow wave structure adopts a high-pure vacuum smelted molybdenum helix of 0.13mm*0.26mm, the helix at the output section of the slow wave structure has a plurality of sections with different thread pitches, and a two-section carbon film attenuator is selected for inhibiting self-oscillation. The slow wave system has the advantages of large coupling impedance, strong heat dissipation capability, high interactive efficiency and the like, and is suitable for the space travelling wave tube.