Abstract: In this paper, the high frequency characteristics and backward-wave oscillation characteristics of the ring-loop structure are studied in detail. Through MTSS simulation, we find that the fundamental-wave coupling impedance of the ring-loop structure is much higher than that of the Helix; at 10.65 GHz, the saturation gain of the ring-loop structure is 10.28 dB higher than that of the Helix; at 10 GHz, the star-oscillating current of the ring-loop structure is 2.35 A higher than that of the Helix, and the star-oscillating length of the ring-loop structure is 53 mm longer than that of the Helix with the same size.Besides, in X-band, the simulation results show that the star-oscillating current of the ring-loop structure and the Helix decreases with increasing frequency, the star-oscillating current and the star-oscillating length of the ring-loop structure are twice over that of the Helix; the general rule of influence of ring width and ring height on the high frequency characteristics of the ring-loop is obtained by CST. The result show that the ring-loop has good performance and is not likely to generate backward-wave oscillations, which has broad application prospect in high power traveling wave tube.