Photocatalytic CO2 reduction is considered as an efficient approach to reduce greenhouse effect and overcome energy crisis. Herein, we successfully fabricated 0D/2D Au/TiO2 plasmon Ohmic-junction composites, which exhibit excellent photocatalytic activity of CO2 reduction to CH4. The main reduction products of the optimized 0D/2D Au/TiO2 heterojunction are CH4 and CO obtained at the rates of 70.34 and 19.75 mu mol.g(-1).h(-1), respectively, with 80% CH4 selectivity. Transmission electron microscopy, UV-vis diffuse reflection spectra and photo-electrochemical tests along with density functional theory calculations confirm that the improved photocatalytic CO2 reduction performance and high CH4 selectivity are attributed to the synergistic effects between plasmonic Au NPs and Ohmic-junction of Au and TiO2, which can effectively enhance the separation and transportation of photo generated carriers and promote a multi-electron reduction reaction of CO2 and H2O, resulting in high selectivity of CH4 generation. These results also indicate that the Au/TiO2 plasmon Ohmic-junction can act as a highly effective CO2 reduction photocatalyst for future applications of energy conversion.