The invention belongs to the technical field of nano material preparation, and relates to a preparation method of cuprous oxide nano octahedral materials. The method includes that copper lactate serves as a copper source; steps of basic solution preparation, PH regulation of the basic solution, conductive substrate process and CU2O nano octahedron preparation are included; an aluminum sheet which is preprocessed and has a surface with scratches or a rough surface serves as a nucleating point of particle growth of the CU2O nano octahedron; the prepared copper lactate basic solution has 3mol/L of lactic acid concentration and 0.4mol/L of copper sulfate concentration; then sodium hydroxide with a concentration of 4mol/L is used for regulating PH of the basic solution to 9; the aluminum sheet which is processed by the conductive substrate and has the surface with the scratches or the rough surface is immersed into the copper lactate solution, heated for 30 minutes at a constant temperature in a water bath at a temperature of 60 DEG C, and the CU2O nano octahedron with an average size of 150nm is obtained. The preparation method is simple, reliable in principle, low in preparation cost, small in energy consumption, good in material performance, and wide in application range.