The invention provides a method for preparing polyhedral cuprous oxide nanometer granules. The method adopts a chemical solution method to prepare polyhedral cuprous oxide nanometer granules comprising cubes, chamfered cubes, cubic octahedrons, chamfered octahedrons or octahedral series. The method comprises the following concrete steps: copper salt is dissolved in water and stirred at a temperature between 50 and 60 DEG C; polyvinyl pyrrolidone, strong base solution and ascorbic acid solution are orderly added, stirred at a constant temperature between 50 and 60 DEG C and kept for 1 to 3 hours; after the reaction is over, the centrifugation is carried out; and a large amount of the deionized water is used for washing, and the cuprous oxide nanometer granules can be obtained after vacuum drying. By regulating the adding amount of the polyvinyl pyrrolidone, the polyhedral cuprous oxide nanometer granules comprising the cubes, the chamfered cubes, the cubic octahedrons, the chamfered octahedrons or the octahedral series are obtained. The method has the advantages of moderate condition, simple operation, low cost, high yield, controllable shape, and so on.