A high efficient MgO∶PPLN ridge waveguide for mid-infrared difference frequency conversion based on the reverse proton exchange (RPE) technique was proposed to overcome the shortcomings, i.e. weak mode field confinement, low mode field overlap, of the traditional annealed proton exchanged (APE) ridge waveguides. Moreover, the index profiles of the waveguide become nearly symmetric after the RPE process, which is benificial to control the distributions of the fundamental and the idler light mode fields and then enhance their overlap factor. Our simulation results show that, the fundamental mode profiles of all the pump, signal and idler lights are located in the center region of the novel waveguide. Accordingly, the mode overlap factor is increased from 0.2714 to 0.4614μm-1 and the mid-infrared conversion efficiency is 2.98 times higher, compared to that of the APE ridge waveguide. Such results may provide reference and guidance for design and development of new high efficient waveguide devices for mid-infrared difference frequency conversions.