Abstract: A nonresonant clinotron based on a metal-grating-shape ridge loading type rectangular waveguide slow wave structure is proposed.The high frequency characteristics of the slow wave structure are studied,and the high frequency characteristics are compared with those of the rectangular waveguide grating slow wave structure.A nonresonant clinotron based on a metal-grating-shape ridge loading type rectangular waveguide slow wave structure and a nonresonant clinotron based on a rectangular waveguide grating slow wave structure are designed.The output characteristics of two kinds of the nonresonant clinotrons are simulated by PIC simulation software.The simulation results show that the output power and the electronic efficiency of the nonresonant clinotron based on a metal-gratingshape ridge loading type rectangular waveguide slow wave structure are higher in the same operating frequency range.