Improving CO2 adsorption capacity, suppressing the recombination of carriers, and extending the light absorption range are key challenges for obtaining high efficiency photocatalytic conversion of CO2 with H2O as reducing agent. In this paper, we proposed using noble metal Ag and activated carbon obtained from biomass with high CO2 adsorption capacity to modify TiO2, thus assembling a TiO2/AC-Ag ternary composite photocatalyst via using ultrasonic and situ photodeposition methods. The TiO2/AC-Ag displayed six times increase in CO yield compared to that of pristine TiO2. The enhanced CO2 photoconversion performance can be attributed to the following three factors: (1) The activated carbon not only leads to enhanced CO2 adsorption capacity due to its properties and high surface area but also makes the electron transfer to its surface due to similar conductivity to metals derived from diverse electronic structures of activated carbon, thereby suppressing the recombination of photo-generated electron and hole pairs. (2) The oxidation reaction sites of H2O are located on the surface of TiO2 and the reduction reaction sites of CO2 are on the surface of activated carbon; the effective separation of two reaction sites remarkably inhibited the reverse reaction during CO generation. (3) The surface plasmon resonance (SPR) of Ag enables the materials to absorb light in a broader spectrum.