Atomically thin, single-crystalline InVO4 sheets with the uniform thickness of similar to 1.5 nm were convincingly synthesized, which was identified with strong, low-angle X-ray diffraction peaks. The InVO4 atomic layer corresponding to 3 unit cells along [110] orientation exhibits highly selective and efficient photocatalytic conversion of CO2 into CO in the presence of water vapor. Surface potential change measurement and liquid photoluminescence decay spectra confirm that the atomically ultrathin structure can shorten the transfer distance of charge carriers from the interior onto the surface and decrease the recombination in body. It thus allows more electrons to survive and accumulate on the surface, which is beneficial for activation and reduction of CO2. In addition, exclusively exposed {110} facet of the InVO4 atomic layer was found to bind the generating CO weakly, facilitating quick desorption from the catalyst surface to form free CO molecules, which provides an ideal platform to catalytically selective CO product.