The invention discloses a slow wave structure for high-power output of traveling wave tubes, and belongs to the field of microwave electric vacuum. The slow wave structure comprises a cylindrical metal shell, a plurality of concentric open metal rings arranged in the shell, and a metal support structure for fixing the metal rings. The support structure of the slow wave structure is made of a metal material, and can achieve a function of heat dissipation to a certain extent. Within the working frequency range, the slow wave structure has a much larger coupling impedance curve than a helix slow wave structure, and can achieve well and effective interaction and exchange of energy. The problem that the coupling impedance of a general slow wave structure is too small is solved to a certain extent. The slow wave structure of the invention is easy to machine. The problem concerning high power output of traveling wave tubes with larger bandwidth is well improved. The application scope of travelling wave tubes is expanded.