An open ridged loaded folded waveguide slow-wave circuit has been proposed in this paper. By removing the metal boundary of the straight waveguide, an open structure has been formed to reduce the dispersion, while the ridge has been loaded to improve coupling impedance. Compared to the conventional structure the improved circuit structure not only increases the interaction impedance significantly but also keeps the dispersion characteristics well. Especially in the high-power design the coupling impedance is nearly doubled.