The invention relates to delafossite structured CuMnO2 powder and a preparation method and application thereof. The preparation method comprises the following steps: S1, dissolving divalent copper salt and divalent manganese salt, adding citric acid and PEG, stirring for dissolving, and adjusting the PH value to 2 to 3 with NH3.H2O, so as to obtain a reaction precursor; and S2, drying the reactionprecursor, grinding into powder, and performing annealing treatment in the process of heating to 900 to 1,200 DEG C at a heating rate of 5 to 15 DEG C per minute under an air atmosphere, maintainingthe temperature for 4 to 6 hours, then performing heat preservation at 1,000 to 1,200 DEG C for 2 to 4 hours under an inert atmosphere, and cooling. The preparation method provided by the invention has the advantages of short cycle and high purity, and is suitable for large-scale preparation and favorable to industrial production; and the CuMnO2 powder has high hole mobility, good photochemical stability and high conduction band energy.